Debate Accepted!
4 against a good 50 edos seems unlikely to me. Madara and Itachi alone are more than enough to keep Hashirama busy. The Third Raikage can be bested by Minato with precision but with so many other respected and feared ninjas using their own abilities around him, I don't see Minato being able to hit that blind spot like Naruto was able to when everyone was just standing around watching him.
The 4 Kage are all really strong sure but they're still just humans. Hashirama is outmatched by Uchiha duo, I do not see three men being able to defeat such an impressive army. So many different ninjas and so many different techniques all happening at once (a lot of which they won't even know) the chances are so ridiculously against them. Quality over quantity wins in this scenario because not only is the quantity so much higher but the army has quality AND quantity.
The legends have been hyped way too much if these three ninja alone can top everything we've seen so far (literal flying ninja, atom dismantling, huge nuke-size detonations, trollkage tactics, lots of kekkai genkais, the 7 Swordsmen and their very specific, very tricky tactics, the TAILED BEASTS and that's not even mentioning Nagato.) No three ninja other than involving the Sage himself could defeat Kabuto's army in my honest opinion.
I always find this topic interesting.
Before we begin. Argee to disregard kabuto and orochimaru input? This is edo vs edo. Kabuto and Oro have no input in this.
I'm also not considering the jinchuriki as part of Kabuto's edo army as they were never under his direct control and were taken by Tobi.
Starting argument
Firstly, Edo Hokage Are 4 S+ Shinobi. They were the best of the best of their time:
Hashirama owned all in his day.
Tobirama survived where the 2nd raikage couldn't
Minato was renowned and had flee on sight orders when no other person had
Hiruzen was renowned as 'god of shinobi' and 'greatest kage' of his time. <- I'm not much into hiruzen or his hype so feel free to dispute this as baseless hype.
On the other hand, Edo Army are a selection of Jonin to S+ Shinobi
Jonin to S- Shinobi
7 Swordsmen and haku, Leaf Shinobi, Kimimaro, Toroi and any other I neglect
S Ranked Shinobi
Akatsuki(excluding Nagato), Kages, Hanzo, Pakura, Kinkaku and Jinkaku
S+ Shinobi
Nagato, Madara
This Analysis is My opinion for this debate and you can swap it around slightly but it seems pretty accurate. Though I do consider 3rd Raikage as possible S+ because of his 2 day, 10k ninja feat. I consider the S+ As those who possess incredible strength; Such As madara who fodderized gokage. Hashi who beat EMS madara. Nagato who destroyed the leaf... etc. I'd put hiruzen at S if not for his hype and I consider Tobirama S+ For the fact that he is brother of hashi, killed MS Izuna and did survive Gin and Kin when they were able to kill another kage. Minato did fodderize 50 in 5 seconds and punked Ay and Bee, so there's that.
Now, The First thing we have to consider in this edo fight is information. Which side has the most information on the other? For me that would be the hokage.
Hokage
Minato - No one knows of him in this edo lineup. None of them are within his time, and those who were are alive right now. At best, Zabuza and leaf shinobi are the only one's who have even heard of his hype.
Hashirama - Literally no one on the Edo Army, except for madara and kakuzu, have information on this guy. The best they have is "God of shinobi". "Beat Madara". And basic Hype.
Tobirama - Very Few Have information on this Titan. Kinkaku and jinkaku, Madara, Muu and Mizukage are the only ones who know of him and his abilities. Everyone else knows his suiton hype
Hiruzen - Everyone should know of him. Whether they know of his skill is debateable. But they should be familiar with the guy. He is the most known person on this team, but the most support.
Edo Army
Nagato - No information. No hype. A ghost. This is why i consider him the biggest threat. I consider him more a threat than madara because of his mystery.
Madara - Both Tobirama and Hashirama have information on him, but they do not know of his new abilities, making him a massive threat.
Gin and Kin - Tobirama has shareable information on them and the only threat with them is the sage weapons. As we've seen, they can be relieved of those weapons and they were defeated by a jonin. They aren't much of a threat, but their mystery make them a contender
Kage - Mizukage and Muu are known by tobirama (They spoke of him when they were revived). 3 Raikage is potentially a mystery. 4th kazekage is known by Hiruzen.
Akatsuki - Shrouded in mystery but easy to figure out. Kakuzu is known by hashirama, Deidara is easy to understand what his attack style is like and sasori is a fodder edo (sorry but he was troll revived

- no puppets lmao)
Itachi - Hiruzen has shareable information
All Jonin to S- - Hiruzen has information on all of them except possibly toroi and chiyo. the 7 swordsmen, leaf shinobi are all familiar to hiruzen and known during his time
So, From this we can see that 3/4 of the hokage are a potential mystery for the edo army. That's a problem because that's almost the entire team.
We must also consider who is actually going to fight. All the hokage are
definitely fighting for the mere fact that madara is on the opposing team. They will make it their mission to bring him down before they quit. By extension, they'll have to defeat the other edo's who will stand to fight.
On the edo team. The leaf shinobi are instantly out of the fight. They won't battle if given free will by kabuto. Kabuto isn't able to precisely control all the edo's at the same time and he's said that he doesn't know alot of their abilities. A few of the edo's will have to be given free will, and even if the leaf shinobi aren't... they won't be effective.
Hokage's Offence
Madara and itachi are definitely not enough to keep hashirama busy. He was able to take on kyuubi and ems madara with relative ease. Hashirama will be able to offer bits of help from time to time. Nagato will possibly have to triple team hashirama. But I agree that he will be a moot point in this battle
The other 3 hokage definitely have enough potential to beat the remaining edo army.
The List of Jonin to S- Ninja I stated before are easily taken care of. They revolve around an attacking style. There are no Defense heavy shinobi on that team and their attack style is mostly that of killing opponents. This won't work on edo's and will lead to their downfall. These ninja will be taken out with relative ease - including the 7 swordsmen. A team effort will cleave out these weaklings quickly. Infact, Itachi, Nagato and madara are the biggest defense force there and they're kept busy by hashirama. Zabuza's mist will not offer any protection for the edo army. Tobirama and Minato are exceptional sensors and it is highly likely they will find their enemies with ease. Hiruzen has also shown some sort of sensor feats (blocking edo attacks during infinite darkness jutsu during orochimaru invasion), but he has not been stated as being a sensor so it doesn't matter. Minato and Tobirama are enough of an attacking force through the mist. Hiruzen's earth jutsu, fire jutsu and water(? forget his other nature) jutsu prove sufficient defense.
The S class shinobi are a bit more effort but will be sealed soon by the trio. There really are no shinobi among them versed in sealing techniques except for kin and gin. This 11 v 3 will be over with more effort, but will definitely be over. The combination of S/t, Frogs, Enma, and Massive walls of water will quickly restrain Akatsuki, and pakura. The raikage is blitzable by minato to pull off the same thing naruto did. Muu is easily taken down by tobirama and minato, and the kazekage is a non concern - He'd cause these few to take longer to fall since he can use his gold to defend a few of them. In the end, Mizukage will be the biggest challenge because of joki boi and genjutsu, but between frogs, 2 exceptional sensors, large scale water attack and the professor, the real mizukage will be found and sealed, with joki boi being distracted by the frogs alone. Joki boi is fast, but he won't be able to touch the hokage, they have too many defense jutsu's among them.
On the onslaught, Minato's skill with sealing jutsu will be the downfall of the edo's. Hiruzen and tobirama may also possess some sealing jutsu which they may perform on the jonin to s- ranks
If Hashirama is still not defeated (shinshusen probably will help against that ever happening), he now has back up. It's Turned to a 4 v 3 and the hokage win.
Hokage's Defense
Nothing the edo army have will hit the hokage. The edo army will have the work cut out for them. Tobirama single handledly blocks the assault of just about all the edos with large scale water attacks. And FTGs allows for quick, precise attacks
Minato will not be hit by any of these edo's due to his superb reaction time and FTG. In conjunction with tobirama and hiruzen, he can easily mark targets and get help throwing shurekin. Large scale attack are redirected back to the edo army with S/t barrier and Toad summons increase the defensive and offensive force they possess.
*Minato does possess barrier techniques, but since these have not been shown, they will not be discussed. Raised point, but please disregard it.
Hiruzen is able to offer a massive defensive support with his array of earth and first jutsu. His shadow clone and shadow shuriken technique increase the pressure on the edo army. Hiruzen is the only one among all these edo's who's been shown to possess shadow clone and this will help tip the scales in the hokages favor. Hiruzen can easily defend his team mates and himself with shadow clones, alongside enma for support
Hashirama is a non discussion. We know what he can do, but Itachi, Madara and nagato may have potential to seal him. Remember, He is an edo. Killing him isn't a factor, sealing him is. That will make it alot hard since hashirama has Mokuton clones. Even if Madara creates some also, it would only increase madara's attack potential and not nagato's or itachi's.
Conclusion
The Edo Hokage's Infinite Chakra. Forbidden Techniques. Summonings. S/t Jutsu and more will help them contend with edo Army.
Hiruzen's Shadow clones, Minato's Frogs, and tobirama's large scale water attacks are enough to help balance out the numbers.
As you said, it's quality over quantity. Edo army is basically Quantity. When it comes down to it, their quality is only as big as the edo hokage's own. They only have 2-4 quality ninja to the edo hokage's 4.
N.B 'Hokage's offense and defence' are a bit of a summary. I want to give you time to respond and i've been typing too long. This is alot to contend with, plus I want to hear what you have to say if you're still here... I understand I didn't explain how exactly the S Rank Shinobi are going to be beat by 3 guys, I just said 'they are', basically. I'll wait for your responses before I state mine.
Hope you enjoyed the read, and feel free to disprove everything I've Said. Keep the flaming to a minimum XD
Edit: I realize i brought up the kabuto point with leaf shinobi. Sorry about that, but you can assume they're working at full power also for some maniacal reason.