call 2 back with the 4th nuts?

I would raise the flop, turn is fine, and call the river 2-bets to you. I would say you have the best hand more than 22% of the time here. UTG+1 could easily raise with the straight, hi-jacks 3-bet is a little worrisome, but I'm not folding the flush here, as either player might just be aggressive enough to raise/3-bet 2-pair, set, or straight.