If you think the owner prefers not to get children in the house you are alowed to lie, masquerader skills could help. It is definetely not their busines if you plan to be pregnant as long the flat is suitable to have children. Of course in a flat share probably a breach of contract if you mutliply yourself, you will have to find something else.
There are some circumstances where a family is favored.
I don`t know about the question if married or not or what citicienship the spouse has. But i doubt it is the owners busines asking about the citicienship of the partner.