Unable to add new member to Family Sharing after deleting duplicate account

I have my wife and three older kids set up with family sharing. A couple of years ago, one child had a second account created that was never used, but it was added to the family - thereby filling all six roles in the family sharing option. Now my youngest has a device that I want to add into the family.

I have successfully deleted the duplicate account and I only see five individuals (including myself) in family sharing. I have tried daily to add my youngest but the option to add a new account is greyed out, even though it’s been a couple of weeks.

When will the sixth spot re-open back up so that I can add my youngest.

[Re-Titled by Moderator]

Original Title: Family Sharing messed up