You answered the question yourself, unless you get a TELL. He has you beat, as these old buggers dont pot into 4-way with AK and worse...The only logical hand you beat is JT, and that should either have been a bet by him as he is IP or just a call OTT.

Actually I think he wont even have that hand, since he might be scared you having Txxx and drawing higher boat, so he should 95% bet it OTF.

What do you think about $100 turn bet? Should hero use different sizing? Also what do think about checking the turn? Range advantge to utg+1 right?

Given other two people in the pot if villain holds QQ or JJ would he pot it to force them out of the hand? Potting the nuts doesn't make sense to me. Still easy to raise small and get money in on the river.

fold he's got the over full

First off this might be a fold preflop in this game structure. You have to be extremely tight in SB and BB when BTN can straddle.

Turn bet is fine I think. You likely have the best hand here and you block QQ. I'd bet a bit smaller because I want to get more calls from straights (mostly AK), but probably not a big difference in EV.

As played I'd fold. Can't think of a worse value hand that he's raising here with, and people just don't bluff like this often.

preflop is not even close, clear fold.

i really don't understand the check on the flop against three opponents...

i dont mind a smaller size on the turn to make straights indifferent, if you bet $60 and this is what I presume to be a weak live game, you are going to get value from all tx, AK and maybe some k9. There aren't many rivers you dislike other than a K or a J, so protection isn't relevant.

Preflop it's a fold. In a limped pot IP, i don't mind overlimping. Or if you are btn straddle and there's been a raise, you are slightly discounted so it's probably fine, especially when all these pots are MW

Thanks everyone for the responses, this was one of my friends hands as I don't play PLO, but I thought it was a nitty fold. My reasoning was that with two other players behind the OMC, he would want to keep them in the pot with worse hands and get more value. My friend did fold, but if he is folding this hand, what is the point in villain raising the turn? After he folded, one lady said she folded QJ, so takes away quite a few other combos basically only leaving 1 combo of JJ that he loses to. Makes me wonder if OMC spazzed out with a hand like J10 here.