Apple Watch Setup

The Family Setup feature allows your family member who doesn't have their own iPhone to use their Apple Watch to do basic things like make phone calls, send messages, and share their location with you.

"Note that some Apple Watch features depend on having a companion iPhone, and aren't available on an Apple Watch that you pair using Family Setup."

And see the 'Availability of features and apps' section in:

Set up an Apple Watch for a family member - Apple Support

I don't know for sure. I suspect it might depend on the app. It could get confusing if an app was controlled by multiple watches when it wasn't meant to work that way. If you want a definitive answer, I suggest you use the 'Get Support' link at the top-right corner of this page.