Help with transferring/migrating Minecraft user account to another MS account

Hello everyone. So, I personally know nothing about Minecraft. My 9 year old plays it on his iPad, and has been wanting me to setup his 5 year old sister with an account. So today, I sit down to do this, and I realize that my son's Minecraft account is actually tied to MY Microsoft Live account, which has a lot of software/business subscriptions. Kinda scares me that my son has login info for my account. He has made purchases, gained coins, etc that he doesn't want to lose, and there doesn't seem to be a way to transfer the Minecraft portion to another Microsoft account if I make a new one for him. This seems a little crazy if this is true, so this is my first question. Is there any way for him to retain his Minecraft user but detach it from my MS account? I see that there is some 'family' account settings where it appears you can add children/new accounts under a MS live account. Wondering if I add a new account for him under my MS account, that maybe this way I can transfer his settings to him. Sorry if this is commonly asked, I just don't know anything about Minecraft.