I think “occupant” or “resident” are both better choices over “owner” for how this conceptually works.
If a family live in the house, then a child of the family could certainly invite a vampire in, despite the child not being the “owner”.
This.
It’s normal here (UK) to write “not at this address” and put it in a postbox. It will be returned for free, and this specific wording lets the sender know it was rejected because the person doesn’t live there anymore (rather than because you’re simply rejecting it)
I’d argue no, because they are not a resident. They are only a visitor.
Occupant in a housing sense is pretty synonymous with Resident legally, but in a wider sense can also mean “anyone there at the time” - especially in non-housing contexts (e.g. the occupants of a vehicle). So for the sake of eliminating all ambiguity I’d strike out Occupant, and stick with Resident as the most appropriate term.