Assistance with moving a child to a new family group

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Previously, my wife and I maintained separate family groups. I removed one of my son's accounts from my wife's family group, after which she departed the group. Now I want to transfer my son's account to my family group. However, despite my wife joining my family group, my son's account still appears as a member under her previous group. As my wife is now a member of my family group, she is unable to remove my son from the old family group.

Is there a method to disassociate his account from the old group and associate it with the new family group? Any guidance would be greatly appreciated.