They can communicate telepathically with each other, so her disguise shouldn’t fool them. Also, if they see Saturn die in front of them, how could they be fooled by her?
Imo Kuma might sacrifice himself to get Saturn off the ship (tho idk if that’s necessary since Luffy is still in G5), but it’ll be revealed that the Gorosei aren’t actually DF users and can still pursue them despite the water, and then Kizaru will come in to sacrifice himself and buy the SHs enough time to get away