If you're planning to have Edwin and Minsc in your party for any length of reasonable time, it probably WILL happen, especially if you're doing a lot of the side quests. Remember that while Good Alignment Fighters are a dime a dozen, you don't get that many Chaotic Evil Pure Class Red Wizards of Thay.
An obvious sign is when you first meet Edwin, if Minsc is in your party, he will complain and try to attack the enemy of Dynaheir(his witch). Of course, you'll restrain him (he doesnt ACTUALLY attack Edwin, it all happens in text) but throughout the game he'll complain. If you add Edwin to the party while Minsc is still in it, he'll complain about having to work with Edwin and the usual when one character has to work with another character he doesnt like.
For a full list of NPC interactions, check out
www.gamebanshee.com
Hope that helped!
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Why?