9Four

You being oop I think the utg played would have put you on a very tight range with your max raise pf. When the board comes two tone and somewhat connected on low cards, personally I like the small cbet... however in this situation it still allowed the villian to 3bet and set you all in.

While a low rundown is unlikely to be in his range, and I would almost never give him credit for two pair here... I think it is possible that he has something like 89TJ or 89QJ. Especially if the money goes all in multiway those hands do great against your AA. Perhaps he had an unlikely AA54 with the nut FD worst case.... I think you could find a fold.

Edit: And it's unlikely you are up against good KKxx like that since there was no 3Bet of.

The only hand that you could possibly be behind in terms of equity on the flop is top set with a backdoor flush draw. And the money already in the pot here means that even of he raises over the top and you have to jam it can't be -EV.

That being said the fact that there are more people in the pot can actually increase your equity, in the case two of them have sets you are pretty ahead. In my mind I can't really see any play here except for jamming hoping to get called by worse and if you are unlucky close to flipping with a set.

This is my first reply so just take this as an idea being shot at you rather than an answer. I think it was a mistake to cbet this flop in retrospect, sure the flop looks pretty haggard and taking it down right then and there seems like a good idea. But I am pretty sure, if he had reggish stats that his call cbet stat is pretty high.

When you pair that information with the fact that you are building the pot on the flop with a bare overpair and backdoor FD, it seems like it sets you up for a lot of awkward decisions later on since his calling range is now very strong and he has position on you. When you are building a pot like that there are only a few cards in the deck that can turn and you will feel comfortable on, a 5 and an A.

His range on the turn now is very strong and you are right, it is almost definitely 2 pair heavy with some low draws in there, maybe a set of jacks he is slowplaying. I would probably do what you are suggesting and barrel the river small at-least making him think a little longer before he calls with 2 pair giving you a little fold equity back.

However my overall take on this is that you accidentally made the pot too big with a hand that isn't really strong enough by betting the flop when it probably made no difference which has made all subsequent decisions more difficult in terms of defending you range.