I feel like Kaido will betray the big mom pirates. Why didn't Kaido just kill big mom when she was chained in sea stone? I suppose it could be because he respected her and wanted to take her down in a true fight, but he also respected Oden and took him out with a cheap shot.
Imo the reason why Kaido didn't immediately kill big mom is because he wanted to take out all of the big mom pirates all at once. imo Kaido invited all of the big mom pirates to the fire festival and then is going to poison their food in order to kill them.
As we know, the SHs actually have somewhat of a connection to the big mom pirates. Luffy respects katakuri and likely considers him a friend, Pudding and sanji have their own relationship, and then you have Nami and zeus, the latter who is tied to the soul of big mom. If big mom dies, it could possibly kill zeus as well.
Kaido will poison Big Mom, the big mom pirates will retaliate and Big Mom will slash kaido with napoleon, severely injuring him. Big Mom and her crew will then be taken out of the war for the rest of the arc. Their poisoning will be the motivation for Luffy, Sanji, and Nami to take out the beast pirates.
I also think its very likely that Kaido could have had his son with big mom. We know that Kaido owes big mom a lifelong debt, however we do not know what this debt is. Could it be that Big Mom had a son for Kaido? If this is true, we could also see Kaido's son joining the alliance once he realizes that Kaido poisoned his mother and siblings.