My oldest child, who is the only one who could have somehow taken them over, never had an iCloud account, so we are stumped. Stumped with three bricks.
It was a nightmare of two trips to the apple store and all sorts of machinations. This was a machine she bought direct from apple. They acknowledged this. There are certainly some issues with their processes which seem to make machine single owner.
I hate being held hostage to a corporation. Anti-theft mechanisms propagated from a corporation should be understood to generally benefit the corporation first (monopoly on resale market) and the user second (limited protection from petty theft).
I know I'm charmed to live in a place where petty crime is relatively low, but these sorts of "lock it to my Apple account" anti-theft tools feel awfully similar to the use of martial law. It's very helpful in limited circumstances but should never be the default state of our lives.