Xbox Remote play console removal or account disable permissions.

If he no longer has access to his consoles then he can't remotely remove them from his account. Here is the quote from Xbox Support website,

If you no longer have access to the Xbox One console where you saved your Microsoft account, you won't be able to remove the account remotely. However, you can change your password, which will disable
access to your Microsoft account on the console to which you no longer have access.

Hey there!

Nice to meet you! I'm Darhyl, a fellow gamer. I'm sorry you are experiencing this. I am here to help.

To answer your inquiry,

In order to disable it. you need to go on to their account, go to settings>devices&connections>remote features. And turn off the remote features that works, however, the owner can always go back and enable it.

The only best option to remove it is to remove their account from your Xbox (this doesn’t remove a game share if you have one with them) by going to settings > account> remove accounts. And then select their account.

Thank you for your time. I hope you have a great day!

Reference link: https://answers.microsoft.com/en-us/xbox/forum/...

Unfortunately, there is no way to remotely remove your account. What you can do is either change your password for your account and that will disable it on their console or you can implement a passcode requirement when you sign on.

Hello LemonMermaid394,

Thank you for opsting on the Xbox forums. We understand that you are interested in learning if you can

remotely remove your account from a console that you do not have access to. If
you no longer have access to the Xbox One console where you saved your Microsoft account, you won't be able to remove the account remotely. However, you can change your password, which will disable access to your Microsoft account on the other console.
The support article we provided explains how to complete this process. We hope this information helps!

Try disabling the accounts Parental Permissions first, then make the purchase from his account. Afterwards, reenable the Parental Permissions. Another work around (If you have separate consoles) is purchasing Game Pass on your account and setting your Son's console as your Home Xbox. This will allow for Game Pass Access on both consoles.