“1. Why ISN’T it permissible to attend the simcha? Just avoid the sanctuary, which is where we’re forbidden to go, not necessarily the simcha room. I know of many Orthodox couples who in years past got married in conservative shuls. It was commonplace up until the ’90’s “
Realistically, it is only a “Conservative Sanctuary” when men and women are physically davening together in it. At a chasunah, that is highly unlikely to happen, and it really is no different from any other shul in that moment. Is it assur to daven in a Conservative Shul when there are NO women present?