Change default device used for kids location in Find My App

I am trying to change the default device for the people tab of the Find My app to both of my kids Apple watches, but I cannot seem to figure out how to do this.

If I go into the find my app on their iPhones, under the “me” tab it shows the “my location” as “this device” (iPhone) but I cannot figure out any way to change this. Tapping the “my location” does nothing.

Just as an aside, when I open the Find My app on my iPhone, and hit the “me” tab it shows that the location is derived from both “my iPhone and cellular Apple Watches” (of which I have one) but I cannot seem to edit this either (not that I want to).

If I go into my iPhone settings and choose the “family” tab, I can see a bunch of information about my kids as part of my family sharing plan but they’re still seems to be no way to change the default device used in the Find My app.

One other problem I have that is only somewhat related is that my younger son can share his location with both me and his older brother yet my older brother is only sharing his location with me, but not with his younger brother. I cannot figure out how this happened in the first place, and I cannot figure out how to change that.

Thanks for help on both issues.

Charles