I set a world up and had my daughter's friends join. At first everything works. Then inevitably a user profile gets corrupted. The corrupted profile cannot access the world; if it does, everybody gets booted from realm and realm won't let anybody on for several minutes. Corrupted profile also cannot join other worlds that aren't realm worlds but are broadcasted to xbox live. Issue is not related to device as changing profiles resolves issue for that device.
We have had two more corrupted profiles with users of my realm. Same solution as before seems to be only option: build a new profile from scratch with a different email.