Sharing my XBOX Live Gold

I have Live Gold Signature. I have only one XBox One console and it is assigned as the main one. My kids should be able to access and use my Live Gold. For a short period they were actually able to. BUt the access is cut. I reassigned the console as my
main one and the access got back. This little game kept going and now I am blocked, I cannot assign the console as the main one again and my kids are now without access. Why do I have to renew the assignment of my console as the main one? What can be changing
the assignment? And how do I solve this situation now? Thanks fo any help.

:)