Since at least one person at the table thinks you are a fish, on this super scary board, why not make it look like a steal on the flop with a bet of 2/3rd or something in that range. Maybe SB calls, and then when you check the turn, he pushes. You definitely have to bet with this many people on the flop, obviously.

Given the action, I think your check on the turn is kinduv trappy. If SB is a donk and is chasing the flush draw, you give him a free card as well. I would bet out here again. Obviously, your betting amount is based on feel and history between the two of you. Whatever the case, I'm sure you can come up with a nice number. If he has a pair, he will call you down at least on the turn. And then maybe he does something creative on the river like push you all-in, which would make your day.