how to remove son from old family group I have no access to

Because the old family group is controlled by an organizer account that cannot be accessed, the child cannot be removed directly from that group by another organizer.

Only the adult who originally granted consent and added the child to that family group can remove the child account from that group. If that adult account can no longer be accessed or “doesn’t exist,” the appropriate path is:

1. The adult or appropriate guardian should attempt to recover that original adult Microsoft account.
   • Use the account recovery process described in the documentation: if the adult cannot access their account, they should attempt to recover the adult account.
2. After the original organizer account is recovered and can sign in, follow the normal removal steps:
   • Sign in with the organizer account at https://family.microsoft.com.
   • Select the child in the family list.
   • First select Remove consent for this child’s account if shown.
   • Then select Remove from family group and confirm.

If the original organizer account cannot be recovered, the child account will remain associated with that old family group until the child reaches statutory adult age in the region, at which point the account can leave family groups independently.

References:

• Leave family group or remove members
• Managing parental consent
• How to leave a Microsoft family group
• how to change date of birth child to adult - Microsoft Q&A