I managed to get through to the end of SoA and into the start of ToB with both Minsc and Edwin in my party without them strangely enough, ever coming to blows at all. A verbal argument here and there, but that's all part of the fun, trying different party combinations. I can't say I've used Valygar extensively yet, but his general blandness (for lack of a better word) as a character usually puts me off him and I have dropped him after doing his quests in the two times I've played the game.
Seeming as how you've gone for a nice evil touch to your party, (very similar to my current party in fact) why not even consider getting Korgan instead? Its almost a cliche around here, but he really must be seen to be believed.
Alternatively, the only other thing I'd maybe suggest is that you could always get away with making Minsc your bow specialist and back up tank to your already, potent party.