but I'm just looking for some thoughts.
Here's mine: f**k no.
Forgive my bluntness, Aurora. But ask yourself, how does going to his family function benefit you or your recovery in any way? The longer you stay coupled to him in any way shape or form, you longer you delay your healing process.
Again, you have more than enough evidence that not only is your AXBF a remorseless addict, he's an a-hole to boot.
Cut your ties, keep his family in your heart, and allow yourself to heal.