Christine What's a difference from emergency key? Keyholder should be able to let you out at any time.
curious already answered for me (thx).
Joh If don't trust your aunt make no deal with her.
I'd add that trust often is not a binary of absolute trust vs absolute mistrust, no matter the circumstance. (For the record, Joh, not that I'm saying that's what you claimed.) Yet, I support the general line of reasoning. Either I'd find rules and measures that gives me sufficient trust in the arrangement (particularly keyholder(s)), or I wouldn't consent to it.
Generally, I also could imagine small steps to learn about a certain person. How they behave and handle situations. Like trial periods. For instance, letting them bear the responsibility for 1 single day, or 1 day per week, while the rest of time stays the current situation. When I got a bad feeling at some time, I'd investigate about the reason; and if no reasonable explanation I'd refrain to go further for a time, rather roll back.