Unpopular opinion, but remove personal houses entirely and make them FC only. Then have requirements of active membership of a certain number of individual service accounts; something like 2 for S, 4 for M and 8 for L. Not that demanding. Something like each active member must log in once a week…if at least 2/4/8 do among members, then all good.
Problem is I don’t think SE even keeps track of what characters are tied to what service accounts in most things. It’s very easy to get around what restrictions there are (1 FC house per service account officially is kind of a joke)