Soldering brass is not difficult -- pretty easy actually. In my youth, slot cars were a big thing and invariably those of us who wanted the fastest cars made our own chassis, usually brass, and wound our own motors, with silver alloy when it could be had. We used nothing but regular flux that a plumber might use on copper pipe but we were not interested in neat -- just strong and heavy. I do know that brass instruments are assembled using solder to join the various straight and bent tubes and the joins are invisible there so there must be some trick to make that work.
I just did a quick Google search on soldering brass and there are loads of videos and instructional pages on the subject. Have you looked around?