Strava or Slopes App on family plan Apple Watch SE

How can I use Strava on my children's family plan Apple Watch SE. No option is available on the Guardian iPhone account.

I tried using an older iPhone that is not active on cellular. I can link the watch and add apps but the watch will not work with cellular until linked back to Guardian account. However apps are now present but do not work.

This is the main reason I opted for the Apple watch versus the others.

It has only got to be a matter of time before a solution is available...RIGHT!!!! Why would this be asking to Much?