okay, so let's say i have never played with either player, and i just sat down. a few hands in, i have AK and 100bb stack, i raise 4bb, player to my left with 100bb stack calls, player to his left with 20bb stack pushes, folded to me, i should push?

that strikes me as wrong. you didn't say that specifically, though, since the player inbetween had 60bb the first hand. i also knew nothing about the tightness of the shortie.