SB is a loose maniac, so you don't have to worry about him.
However, MP is a tight player, but does have a large limping range, it could easily mean 22, 66 or 88, but I would say 22, 66 are more likely.
I would definitely fold that turn, most of the time when a tight calls you on the flop and shoves on the river he has you beat. Probably slowplayed a set on the flop.