What is the ruling on a father registering his house in the name of one of his sons from another wife, while the house in which the second wife and her children live is registered in his name? And is it fair for the house in which the second wife lives to be registered in her name, especially if she contributed to its construction? And is it considered fair for the father to eat and sleep only at the second wife's house, even though he has not divorced the first wife?

Justice in overnight stays is obligatory without dispute. As for justice in additional spending and gifts, the preponderant opinion is that it is recommended. Your father is not obligated to gift the house he lives in to your mother. Regarding the money your mother contributed to building the house: if it was conditioned upon her receiving a share, he must fulfill it; if it was a loan, he must repay it; and if it was a donation, he owes her nothing. As for the house he gifted to his other wife, if she did not take possession of it in a lawful manner, the gift is void, and the house remains the property of the father, and the wife's disposal of it is invalid. If possession and the gift to the child were completed, then the wife is sinful for favoring her in the gift. There is no harm in the father residing with you only, as long as the second wife is content; otherwise, she would be disobedient. Wives' shortcomings in intimacy are wrong, for obedience to the husband in enjoyment is one of the wife's greatest duties.