Yeah, Law and Yamato are the only 2 actually available to help Jack. Law was on the 1st floor, Yamato on the 3rd. Jack is on the 2nd. Unless Inu miraculously defeats Jack who will probably use hybrid, one of these 2 has to forgo their attempt to fight a Yonko and stop Jack.
At this point I'm wondering if it's Law, because Kid is already stopping Big Mom, while Kaido has free range atm. It might be imperative that Yamato stop Kaido and they have their personal moment. Or the vice versa happens, who knows.