Hi @Emily Chapman !

From Deezer Help Center :

When an Admin deletes a Profile from Family plan, the member's favorites, recommendations, playlists and personal listening history will be permanently deleted. This is why we recommend converting profiles into independent accounts or transferring before the Admin deletes a Profile .
When an Independent account is removed, the account will revert back to Deezer Free. Independent account owners can subscribe to any Deezer plan to access playlists, music on demand and offline listening.

In your case you need first converting profiles into independent accounts or transferring playlists  of each Family plan member .

Then Admin need to delete Profile which will be revert to Deezer free.

Then two profiles which will be in Deezer Duo need take  Deezer Premium  first ,and then take Deezer Duo .

or contact Deezer Support / Chat

https://support.deezer.com/hc/en-gb/requests/new?ticket_form_id=19681539004957