The Ritual Conjuring thread got me thinking about more than one magician banishing the same spirit at the same time. Banishing is Exclusive, but this pertains to each individual, so I do not think it forbids 2 magicians ganging up on one spirit. I really don't see any problems until you get to the spirit resisting the banishment. Then the spirit, which is engaged with the first magician trying to banish it, is set upon by a second magician attempting another banishment. According to the rules, the spirit can take no other actions after the first magician starts his banishment try.

Does the second magician get unresisted shots at banishing? Does the spirit get automatic tries to resist that require no actions? Why?

I don't recall any rules for it, but I believe it -should- be treated like combat. 'Friends in Combat' modifier included. But that's just personal opinion, not canon.

I would do this as a team action with the logic that if you aren't working togther then you are interferring with each other.

I would go with the spirit get to choose who it 'attacks' in the banishing contest, up to it initiative number of actions per round.
Edit: I just realised this pertains to 'scorching' duals arcane between magicains as well.