First off, I'm so sorry about your situation, I can't imagine how frustrating that is. Unfortunately, FamilyWhere doesn't only use GPS, it uses a few different ways to track you, so GPS alone won't block your location. If the account holder insists on keeping the application on your device, having your location on will actually provide a more accurate reading if part of the problem is the results. This site here will give some insight - https://tfw.support.safely.com/hc/en-us/articles/204119066-My-locations-are-inaccurate-
That will yield more accurate results, however the only real way to stop the location tracking is to be the primary account holder and have it removed.
I wish there was more we could do to assist.
Your only other option is to open your own account.