33.33% for each class type as there are only three classes present in your example. loot will only drop for the classes present. the number of each class has no bearing other than taking the place of other classes that could have been there and thus changing your chance because of it.
in other words everyone in the group will have the same chance of their classes gear dropping no matter how many of one class there are.
Somehow I really doubt that. I was in an KP nim ops once and it was like an Inquisitor run only besides me. And it dropped nothing but Inq stuff.
But maybe Im just that really unfortunate guy.