Are houses considered a gift given by the father to his wives, or are they included in the inheritance, and does the mother have the right to remain in the house she currently inhabits, or must she move to the house allocated to her by the father, knowing that it is smaller in area?

Firstly: The father's statement "Every wife has her own house" could mean granting ownership of the property itself or merely the right of usufruct (beneficial use), with the former being more probable. The matter should be reviewed, and the surrounding circumstances considered to ascertain his intention. If you all agree to exclude the three houses from the inheritance and assign them to the wives, that is good.

Secondly: It is incumbent upon a husband to be just among his wives in giving gifts. Therefore, if the father gifted the houses to his wives, he ought to have given your mother a house similar to those of his other two wives, or compensated her for any deficiency in her house.

Thirdly: If it becomes clear that the father gifted the houses to his wives, then your mother's share is the house he designated, even if it is small, and the shared house is part of the inheritance. It is better for the other two wives to satisfy your mother and compensate her for the deficiency in her house, as an act of kindness to their husband and to absolve him.