Need to remove 2 child accounts from family share.

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Get Support          Work through the screens to get a chat option. You may have to pick a slightly different problem.

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This article explains how to move child accounts to another family sharing group.

Move a child to another group using Family Sharing - Apple Support

But as you can't communicate with them you won't be able to complete the steps.

Other than waiting for the accounts to not be child accounts anymore then remove them there is nothing you can do without having access to the child accounts.

The only option left to you is to contact apple as you have done.

Wither they can solve it I cannot guarantee. But you need to try and contact apple support again, and get a final answer.

One of those groups should be the one responsible for giving you the answer.

Contact Apple for support and service - Apple Support

Good luck!