If not being able to pick a label that satisfies them is causing them anxiety, tell your friends to sit down with their child and tell the child they love them regardless, and it's not unusual to feel this way at that age. Tell your friends to tell their child that their feelings can change or evolve over time, and that is okay. They don't
need to find a label either, if they don't want to. Also remind your friends that having anxiety about your child experiencing identity stress is normal, too. I didn't know I was asexual at that age, so I used a different label to explain myself. I just thought I was picky or too busy with high school. I wasn't harmed in the long run thinking that I was something I was not.
That's my recommendation.