I’d go bigger pre-flop. You already have a raise and 3 callers, with $31 in the pot you only bet $35. I’d like to see that above $50, probably closer to $60. Once you get one caller you’re likely to get more, so you have to charge people. KK loses a lot of equity mutli-way.
As for the fold, I have no idea what to tell you. At a bigger game, this is a pretty easy fold. I don’t really blame seat 9 for calling with the Ks. But the donk bet with 42 makes no sense. All I can say is stay at the table and target that guy. He’s going to be giving money away all night.