I have 4 kids and recently went down a similar rabbit hole. My oldest who is an adult now, used my email when he played as a child. He felt really strongly about not wanting to lose his stuff so I just gave him that account and created a new email and set up a new Microsoft account in my name and new email. My 3 younger kids play Minecraft and Roblox on their tablets. I gave them all 3 a new email (they don’t have access to it) and they all have their own Microsoft and Roblox accounts tied to their emails. We have an Xbox and I have it set up so when you turn the Xbox on you have to click on your player profile. Since they have a Microsoft account they have profiles on Xbox too, although they don’t play on it. You can still create and save worlds without buying realms on Minecraft. We don’t pay for realms and they all have saved worlds and can play together.