I think my girlfriend and her exes have hot friends.
Why do you feel that way about them?
Because I'm a guy and can't think of anything else!
It's okay to be attracted to people that you meet in your life, but it is a bad idea to try to get involved with your partner or your ex's friends.  This will make things very awkward for all of you, since you will be showing up to the same events together.
You can't tell me what to do.
I know, but this is advice you should take. If your current girlfriend found out about this she most likely would get jealous and this could cause issues in your relationship.