Who sets the pay for members for congress?

Answer 1

The members of congress.

There's a law (actually the 27th Amendment) that forbids them from raising their own pay directly... any pay increases cannot take effect until after the next election of Representatives. So Representatives only get a pay increase they vote for if they're re-elected (Senators might or might not benefit from their own vote without being re-elected, since Representatives are elected every two years, but Senators have six-year terms).

There's another kicker: there's a law that automatically gives Congress members a pay raise every year as a Cost-of-Living Adjustment unless Congress specifically votes to decline it. For the first few years it was in effect, they did, but they have consistently not not accepted the raise for about ten years now (that is, lately they have not been voting to not accept it, so they automatically get it).