In my experience they NEVER stop for ANYONE - Not even kids - So I would advise you to be very careful how much you drink until you get to the resort - Or take a handy bucket/ bottle with you
Depends where you are transfering to. The longer transfers (Sofia - Pamporovo) stop at McDonalds just outside Plovdiv, and the Plovdiv - Bansko transfer has a break after approx. 2 hours (at least ours did.)