I’m pretty sure when Kakashi tried to use Kamui on Mazou and it didn’t work and he said “Don’t tell me”, he meant that Tobi had used Obito’s right eye to revert Kakashi’s Kamui with another Kamui.
That’s why Tobi can teleport, and that’s the reason he said “Don even try Kakashi” then he was about to use Kamui on Tobi after the fight between Sasuke and Naruto, because both of them have the same eyes from Obito.
(This doesn't mean he is Obito, just he has his right eye, and Kakashi has the left one)
I don't think you need to have Obito's eye, or Obito's father's eye, or any eyes from people related to Obito.
Let's do a thought experiment here. How many Uchiha were there, at the peak? A hundred? A few hundred? A thousand? Let's take the smallest number and suggest it was one hundred Uchiha alive at their peak. And of them, how many would be capable of unlocking an MS eye, if they knew the secret? All of them? Half? One tenth? Let's go with the smallest number. So that's 10 Uchiha alive per generation capable of using MS techniques.
So here's the question: Does each family get their own unique set of MS abilities? What's the limit?
So if techniques are similar depending on family relationship, and if we say that there's an average of two children per family (and unlocking MS is hereditary) then there are 5 Uchiha families with MS, which means 5 sets of techniques that can be used.
So Itachi and Sasuke got the big three: Amaterasu, Tsukuyomi and Susanoo.
Obito's eyes clearly have Kamui but no other techniques (or, Kakashi hasn't used them, or doesn't know how).
Shisui's eye had Kotoamatsukiomi, but no other techniques that we've seen.
Madara, who we have to assume is related to Sasuke and Itachi in some way because of this logic, has Susanoo (but hasn't used Amaterasu or Tsukuyomi yet).
Tobi is using some weird Space/Time jutsu which seems pretty clearly related to Kamui in either size or scope. Does this mean Tobi is related to Obito some way?
So even using the smallest numbers I can reasonably estimate, we still have 5 different sets of MS techniques possible (assuming each family gets a unique set), but in the manga we've only seen three. And besides Kotoamatsukami, these three sets of MS techniques appear to be reused between people with no obvious relationships.
The really weird thing is that Shisui, who was regarded as an extremely powerful and capable ninja, only seemed to have one MS technique that he could only use once every 10 years. This means that Shisui couldn't also use things like Amaterasu or Tsukuyomi? Even though Shishi was known for his prowess with genjutsu, and Tsukuyomi is one of the most powerful general-use genjutsus in existence? It doesn't make any sense that Shisui would only have had one MS technique that was so limited, because Shisui was such a gifted and intelligent warrior.
Let's also look at things from the perspective of the techniques themselves:
Amaterasu: Described as an ultimate, unblockable, unstoppable ninjutsu
Tsukuyomi: Described as an ultimate genjutsu, able to distort the victims very notions of time and space
Kamui (including Tobi's version): Has been described as the most powerful and general-purpose space/time jutsu. Kakashi, the copy ninja with thousands of techniques, treats this like his most powerful technique. Tobi uses it as almost his only battle technique and is using it to fight off four of the most powerful ninja in the alliance at the same time.
Susanoo: Described as an ultimate defense by Sasuke, but also has offensive capabilities described by Madara as being in a class of it's own (perhaps only rivaled by the power of the Bijuu).
Kotoamatsukami: Also described as an ultimate genjutsu. It's effects are more powerful and more subtle than Tsukuyomi, but it can be used less.
So if we assume that the MS eye enables the use of various ultimate techniques, how many "ultimates" can their possibly be? We already have ultimate techniques in the areas of offensive ninjutsu, genjutsu, space/time jutsu and whatever category Susanoo falls into. If there are, by our estimates above, at least two more sets of techniques available to MS users, what other ultimates would they be? Ultimate taijutsu? Ultimate medical jutsu? These things don't seem like they would be eye techniques.
By power of elimination, there really aren't any other areas where there could be ultimate, non-elemental, eye-enabled jutsu. This means that these five techniques listed above, with some variations, are probably the only MS techniques there are. That means that ninja who aren't related to each other, given enough MS users MUST overlap techniques at some point, because there are limited numbers of techniques.
Madara's Susanoo clearly overlaps with Sasuke and Itachi, but they don't seem to be related (considering it was within less than 70 years since Madara died, Sasuke and/or Itachi might have recognized him as being a grandfather or even great-grandfather).
Tobi's space/time technique clearly seems to overlap with Kakashi/Obito's Kamui, but there's no evidence that they are related either.
