How each of the kages counters Uchiha arsenal on their own
Gengetsu:
Gengetsu will start the battle by summoning his clam. This not only makes a mirage of his own body, but mirages of his teammates as well so everyone on his team has their position hidden.
Amaterasu: With the clam producing genjutsu, Itachi and Sasuke will only see a mirage of Gengetsu and won't be able to land Amaterasu if they can't get him in their line of sight. Not to mention, even if he does get hit he can shed off the burned parts of his water body due to Hydrification.
Genjutsu: Can't land genjutsu on an opponent you see, at least it won't be easy since the only way to do it is pretty much on accident. Even if he gets caught, his clam is still on the battlefield therefore his position won't be revealed.
Susanoo: Unfortunately Gengetsu can't really do a thing to Susanoo. Joki Boy is his strongest attack and it can probably be tanked with a ribcage. However Itachi can't seal him with Totsuka due to being unable to locate him.
Rasa:
Rasa will start off the battle by spreading out his sand over the battlefield to put the location in his favor.
Amaterasu: Muu will lighten his gold dust to give it a speed increase, so Rasa can block Amaterasu with his sand like Gaara did at the kage summit.
Genjutsu: To avoid getting caught in genjutsu Rasa can utilize his Third Eye or sand sensing to navigate during the battle.
Susanoo: With lightened gold dust, Rasa can replicate Gaara's feat of whipping the user out of Susanoo using gold dust at his feet.
Muu:
Muu will lighten the Raikage and then Rasa's gold dust at the start of the battle, then go invisible as the clam genjutsu takes effect.
Amaterasu: When Muu is invisible he has a double layer of clam genjutsu + invisibility camouflaging him from the sharingan. Neither Uchiha will be able to get him in their line of sight to use Amaterasu. If he does get hit, he can split bodies to escape though I doubt it will come down to this.
Genjutsu: It's very difficult to land visual genjutsu on an opponent you can't see, especially a sensor who doesn't have to rely on his eyesight. If he does get caught, he can just straight up break out of any genjutsu bar Tsukuyomi given his level of chakra control "kai" release can do the trick. Or he has three teammates to break him out.
Susanoo: Jinton atomizes through any Susanoo. He only needs to prep his jinton behind Rasa's gold dust to prevent Itachi/Sasuke interrupting jutsu prep with Amaterasu, and he also has the Mizukage's genjutsu concealing his presence. Susanoo's attacks aren't any trouble since Muu can fly out of range of its attacks. Susanoo arrows are the only thing which could be able to interrupt Jinton prep but Raikage can attack Sasuke and distract him while Muu attacks from behind him with Jinton. Sasuke would either have to focus on Muu to snipe him with a Susanoo arrow then get butchered by Nukite which tears through Susanoo, or defend himself from Raikage with Enton blade then end up getting vaporized by Jinton.
Third Raikage
Amaterasu: After getting his body lightened by Muu, Raikage gets an incredible speed boost from being as light as a feather. This allows him to dodge Amaterasu similar to how Ay did by exiting the line of sight before he gets hit. Not only that, but there is the mizukage's genjutsu concealing his location making it doubly hard for either Uchiha to catch him in their line of sight and hit him with the attack. Muu will not need to stay on Raikage's back for this fight because unlike Ay's physical punches, Raikage uses Nukite (a chakra spear) which does not need to be made heavy for the attack to be succesful.
Genjutsu: Itachi and Sasuke cannot track the Raikage, and won't be able to land genjutsu due to how fast he is. If they use genjutsu while in Susanoo, Raikage can just look at Susanoo instead of looking at their eyes, and if they use it without Susanoo they get shitblitzed by lightened Raikage.
Susanoo: Nukite will pierce through V4 Susanoo and kill Sasuke. Itachi's Susanoo is more durable since it has Yata, but Jinton can still be used to destroy Itachi's.