Not folding on this flop ever, the fact that it's a multiway pot does make it a little scarier though.

Turn is a prety horrible spot, but to him your hands probably underrepped at this level. Let's have a stab at a range here even though he's unknown.

Board: 6s 6d 9c 8h
Dead:

equity win tie pots won pots tied
Hand 0: 60.128% 60.13% 00.00% 1508 0.00 { QcQd }
Hand 1: 39.872% 39.87% 00.00% 1000 0.00 { JJ-66, A9s, A6s, J9s, T9s, 98s, 76s, 65s, A9o, A6o }

I probably call down here because this is 2NL and as sir P says the min raise on the flop as supposed to the call flop, raise turn line makes me think TP and overpairs are more likely than 6s and boats.
Sucks to be oop here because we don't get a chance to value bet river when he turns his A9 face up by checking.