How would you model a household in Nonprofit Cloud, and why not just put everyone on one account?

I model the household as a group that people belong to, rather than as a record that replaces them.

1. Party Relationship Group represents the household or affiliated group. Group membership and relationship objects — Account Contact Relation for members, Contact Contact Relation for person-to-person relationships, Account Account Relation between organisations, Party Role Relation for the relationship type — connect the individuals to it.
2. Collapsing four people onto one account destroys individual giving history, which matters the moment you want to know who in the household actually gives, who is the primary contact, or who to steward after a bereavement.
3. It also fails the change case. People move in and move out. A membership relationship can end with a date; a merged record cannot be unpicked.
4. The household still earns its keep for mailing, salutations and rolled-up giving totals — which is what household rollups are for — but those are derived views, not the storage model.