I dont know if this will work for Keldorn and Viconia, because I don't know how they start fighting, but the way I stopped Edwin from leaving is that he would always say some comment like "no, I will not suffer this any longer", or something like that, just as an in game comment, no dialouge box or anything, and then leave. If it is similar, simply give the character a command while they are talking, and whatever they were about to do will stop. Similarly, if those two are about to fight, try pausing RIGHT after their dialouge and then giving one of them an orde if they are not hostile yet. Otherwise try dropping one and then picking them back up. Stuff like that. Hope this works for you.
The other problem sounds like a serious bug, maybe a patch will help? In fact, I think I remember reading something like that in the fixes on one of the official patches, for ToB I think. Good luck
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"Not everything ends the way you think it should"