See, the thing is that you can't control other people, what they think and do, or who they're friends with. Controlling friends by placing ultimatums on your friendship is bad for a friendship, period.
It's up to you to decide who you will be friends with and why, what your boundaries are, what you show and tell, and how you present yourself to others. If you don't want to be friends with people who are friends with your ex, so be it. But making hay about what they do and don't do is putting focus on the wrong people, when the only person you can control in this world is yourself.