being that you said BTN has AF 7, and they're both very loose players esp for these stakes i think both their ranges are wide enough that you should never consider insta folding here, true you don't have that much invested yet and MP does have a 137bb stack...

if you bet, MP raises, and BTN re-raises i'd argue more for folding just because it's ridiculously hard for BTN in that spot to have worse than top set or a made flush considering it's 3 ways and your hand could be very strong.

i think calling is best, it keeps their draws in you just have to re-eval and on certain turns muck this thing.