>>87677906off the top of my head for at least a couple of them(basic reason I'm thinking for the harem forming is that it starts out for non-sexual reasons, with Kim and Ron expanding Team Possible in the aftermath of the finale, through both plot and coincidence most of the people they recruit are women);
Shego probably wouldn't be too hard to convince to join(since Drakken and her are good guys now it'd give her something to do)
Electronique got hit by that good/evil machine at the end of her episode so she should still be good
Warmonga I was thinking wouldn't be the original(who died during the finale), but rather a clone created by another villain of Kim's
any other female villain would end up joining in the non-sexual stage when it's just about Team Possible expanding, Global Justice would basically be handing off some of Kim's villains to them as a form of parole(through coincidence they'd all be female)
as for the actual Harem parts, I'd justify it forming and everyone in it being fine with sharing Ron as a side effect of Ron syncing up further with his destiny as the Mystical Monkey Master(so there's some mild magical coersion going on)
overall this is just a rough idea, and nothing is set in stone