Home xbox

Hi, you will need to contact Xbox support and ask them to reset it for you.
support.xbox.com/contact-us

Yes multiple accounts can have one xbox as their home xbox there is no known amount that it can be but I believe there is a limit of like 16 accounts that can be on one xbox at a time

contact official support for this.

the message says you can only have 1 home xbox at the same time en max 3 times a year changing console

but i only have mine i want to have on home,my son has his own gold account now

No he need to put his profile on your console then do the home console switch

However since he already did it 3times he's going to have to wait a year

Or you can have him try support but they aren't obligated to do so