I almost never bother to bring the mothers over to the house. I found it easier to have a male sim visit them instead, probably because my dynasty house was decently big while the houses in town weren't. The only exception was if the mother lived in a house without a double bed or a shower (I don't know if any houses in Union Cove have that issue, but plenty in Twinbrook have no places to woohoo).
As for getting romantic interests, you can get nearly any sim to be a romantic interest even when you have one or several already. You do have to worry about them being accused of cheating, though.