There should preferably be:
- a private bathroom each
- two living rooms in a house where two families live
- a kitchen each
This can seem a bit unnecessary, but with their own space for cooking, toilet matters and relaxing is paramount when trying to maintain privacy.
Try looking for houses with:
- a granny flat next door
- two semi detached houses next door to each other
- a house that can be split up into two portions.
Parents may complain this is totally unnecessary, but if tact and diplomacy is used, this goal can be achieved.