Expect a wobble. Someone may hear rejection where you intended a boundary, and may say so at some length. You do not have to win that exchange; you only have to not reverse your decision inside it. Repeat one calm sentence, thank them for understanding even if they have not yet, and let time do the rest. A code-based lock helps in practice too, because access becomes something you can grant for a weekend and quietly retire afterwards, with no symbolic handover involved.
Is it unreasonable to say no when a parent asks for a key?
No. Declining is a preference about your household, not a verdict on the relationship, and you are allowed to hold it without a detailed justification — "we'd rather keep it to just us, but you know you're always welcome" is a complete answer. If saying no feels genuinely unsafe rather than just uncomfortable, or if refusals in your family are routinely met with punishment, that is worth talking through with a counsellor or someone impartial, because the pattern is likely bigger than the key.
What if my partner won't back me up about their own family?
This is the real issue in most of these situations, and it needs solving between the two of you before anyone speaks to the relatives. Agree on the rule first, then decide who delivers it — as a general principle, the message lands far better coming from the person whose family it is. If your partner will not carry it, ask what specifically they are afraid of happening; often the fear is a scene rather than a disagreement, and knowing that lets you plan the wording together instead of arguing about loyalty.
