[Q..]

I like fold, this way CO would have to win at least 2 pots to get 3rd with pretty random hands (this and the one when bb hits him if he triples up now). That would be roughly 1-0.5*0.5=0.75 for us to get 3rd. 0.5 is rough average chance for CO to win allin against 1 other guy(it would probably be less since when he would be on bb after winning this round he would be facing best hand from out of 3 ppl)


If we call now and bb calls there would be 6 types of outcomes, in stack size order
123
132
213
231
312
321

If biggest stack wins we are 4th, if shortest stack wins and biggest stack wins our side pot(132) we are fourth, we only like it when we win both pots(213,231) and when we win at least side pot against big stack (321)
So there are 3 good(semi) outcomes and 3 bad for us here, if we consider everyone to have roughly 33% to win that would be 50% to bust if we go allin along with big stack, so folding looks much better to me. If our win chances are less then 33% 3 handed then its even worse. If sb joins the party it would be even worse for us..