Tbh judging from law's words this chapter; "We need to remove one of them" combined with Oden's words in his letter to Toki ; "A new powerful new generation will appear in the new world in 20 years,they will be the ones to take down Kaido",it seems to imply no splitting against the emperors,just removing the most irrelevant in the scheme of this raid out of the equation.
Law can just shamble Big Mom away mid-air(we are approaching the flower capital where Kaido seemed to imply the Poneglyph is) and she just goes on Poneglyph hunting.
Or someone just gets Big Mom busy,my point is Kaido is the main enemy and all the rooftop Sn will participate in his downfall.
Expect some 5 vs 1 in the climax; Kaido vs all.