Is the father obligated to prepare rooms in his new house for his married children who own apartments, or is that exclusively for unmarried children? And does the ruling differ if the married daughters spend weeks at the father's house?

If a father gifts his house to his children, he must equalize the gift among them. It is not permissible for him to gift to some and exclude others, unless some of the children have a need that necessitates their preference, in which case preferring them is not forbidden.

As for the mere residence of unmarried children in their father's house, this does not obligate the father to prepare similar rooms for the married children, because residence falls under the category of maintenance and is not a gift; therefore, equalization is not required in it.