To some degree, however, in situations like this (being friends with and enemy of a friend) it is up to you to make clear to all parties your intentions. Communication is key.

From my experiences with situations such as this, the friends of mine who were enemies to each other, were made to understand that each of our relationships were separate. As they were my friends, they keep the matters of their adversaries to themselves.

There have actually been a few times in these cases where the status of enemy was dropped between the adversarial parties, due to the friendship as well.