I highly advise taking the 'supervised visitation' approach.
When we married (not poly) we had a his, mine and ours child dynamic. Dh's mother wanted ONLY DH's bio kids to visit. We told her straight up-'all or nothing with the family'. All holidays were at our home, doors open to extended family with the caveat that they were to treat all members of our household with respect as oir chosen family (we had roommates including my current boyfriend, we just werent poly yet).
That rule was upheld with ALL extended family. Only my mil took issue with it. Her loss. Everyone else found a way to mind their manners, in the process, get to know ALL of us as family.
Her home-her rules.
My family-my rules.
My rules are-all or none, take it or leave it. Invitations that exclude, dont get accepted. Period.
Now that we are poly-same rules apply. No issues. We dont always choose to go out together. We frequently pair off for dates. But family activities are FAMILY activities and that means bf is included. Period.
"Love As Thou Wilt"