1. There is zero proof he fighting an admiral and even if sanji is guess what? Sabo is destined to fight akainu. It's clear as day that that will be sabos opponent. Why? Because of the fact that a mera mera user lost to a superior fruit. Oda is going to have sabo advance what ace could not that will put him on the same league as a fleet admiral.
Zoro is fighting kizaru since I do not think greenbull or fujitora are going to stay as admirals. Infact it would make sense if they two are members of sword. I see them both returning as admirals when the final war is finished. Greenbull may die. While funitora returns as fleet admiral
Sanji will more than likely fight someone from cp0 their top members