What is a mother daughter house? ...
Answers: A mother/daughter is a single family house near two kitchens and two bathrooms, more or less arranged as separate living areas but connected as one overall dwelling element. Most building codes specify that a single dwelling unit cannot be inhabited by unrelated persons, and a mother/daughter is really a single domestic dwelling that happens to hold a separate living area to be precise connected to the other unit. A mother/daughter will typically hold one electric meter servicing the entire building.
By comparison, a two-family house has two separate living areas next to two separate entrances, each next to its own kitchen and bathroom, and each next to its own electric service and electric meter.
Usually it's a duplex of some kind, they hold different names contained by different parts of the country or the world. It could be an upper apartment over a lower one, or two apartments side by side in indistinguishable townhouse.