Can I put my betta in with...?

Well, my male betta is pretty old and he now just sits around doing nothing. Well, I have a female betta sorority tank with five bettas. I was just wondering if I could put him in with them (he's in a crappy one gallon, non-filtered tank and I want him to have a filter and such, but can't afford another tank) I'm pretty sure he won't attack them, but would they attack poor old him? Like gang up on him or something? I really don't want him to suffer any longer in his one gallon crap tank.