Christine What's a difference from emergency key? Keyholder should be able to let you out at any time.
The difference would be that your aunt cannot let out your mother without you knowing it. So secretly having different rules preferential to your mum will not be possible then. So you can be confident that she will honour the agreement of same rules and freedoms (or actually the degree of enforced chastity) and enter into that contract with your aunt with confidence that it 2ill be fair and equal.