Multi-Parent Controls

Hi there. My ex-husband and I would like to get our son a cellular-enabled Apple Watch. We have parental controls set up on devices in our individual home, but this watch would ideally be controllable by whichever parent he's with that day (I don't foresee daily edits, but for purchase approvals, early/late bedtime adjustments, etc). Is the only way to have both parents be able to adjust the Parental Controls is to do Family Sharing? I'd prefer not to do that if possible but - is there a work-around?

And, can I selectively turn off shared purchases with specific Family Members if that's the way we have to go? Meaning, I'm fine sharing apps and whatnot with my wife but would prefer to not share with my ex and his girlfriend.

Thanks!