The couple has to agree before anyone else is told
Nothing goes worse than a boundary announced by one partner while the other is visibly uncomfortable in the background. Before you say a word to anyone's parents, sit down together and work out what you both actually want: whether visitors ring first, how much notice feels normal, whether weekends are open or protected, and what genuinely counts as an emergency.
Expect a difference of opinion. What one of you grew up experiencing as closeness, the other may have experienced as intrusion. Neither is wrong; they are just different family cultures colliding in one hallway. The workable rule is that whoever is related to the person delivers the message. It should be your mother who hears it from you, and their mother who hears it from them. This one convention removes most of the sting, because it stops the conversation becoming "your partner doesn't like us".
Say it kindly, say it once, then hold it
Boundaries do not need to be announced like a legal notice. They land better attached to something warm and specific. "We love having you here — can we make Sunday afternoons our regular thing? Mornings are chaos and we'd rather you saw us at our best." You have given something as well as asked for something, which is what makes it possible to accept.
Then hold it, gently but consistently. If someone arrives unannounced, you can be pleased to see them and still say, "You've caught us mid-everything — give us a ring next time and we'll do it properly." You are not required to escalate. Repetition does more than intensity. The first three times feel awful; by the fourth, it is simply how your household works.
