@MojangSupport very confused. son and daughter with two seemingly identical xbox live accounts under my family - dload mc java on two macs - son logs into one with ms acct. Daughter tries to log in using her account. it's not recognized? We sign up, and it wants her to buy?
I'm sorry to hear this. When only the demo mode is accessible, this means that you're logging in with an account that does not contain a Minecraft profile/username. If you haven't yet, please visit https://help.minecraft.net/hc/en-us/articles/360029643892-Can-only-play-Minecraft-demo-Java-Edition- … for a list of possible solutions.^SJ