My sister and her husband, are using the same Apple ID with their iPhones. When she and I try using Find My Friends App, I can only see his location. Her’s says “follower” but I can’t follow her back.

My sister and her husband are using the same Apple ID with their iPhones. When she and I try using Find My Friends App, I can only see HIS location. Her’s says “follower” but I can’t follow her back.Her location services is on and she receives a request to be followed but only her husbands phone is tracked. She’s not very phone savvy and doesn’t want to get another Apple ID. Is there something I’m missing or something I could do to adjust his phone or hers to eliminate this issue?