Thoughts please

So my ex's sister wants to hang out and see me and I honestly do too because I miss her, and her mom. But I don't want to see my ex, I won't hang around him or talk to him or see him. Has this ever been okay with any of your significant others? I'm currently single but I'm just wondering if anyone has been in this situation. Can you still be friends with your exes family without it being weird? Thoughts?