He gave one of his wives a house with the agreement of his children from his other wife; after he died, they objected. Is the gift valid or is it part of the estate?
Question

                My father died, may Allah have mercy on him. A long time before his death, when he was in good health and completely sound of mind, he gave a gift to my mother, because she was in need and poor – i.e., it was justified – of a traditional house and an apartment building that are registered in one title deed, and a courtyard in front of the building, which has a title deed of its own. My mother took possession of this property when my father, may Allah have mercy on him, was still alive, but that was without any official papers, as it was a gift on the basis of words alone, but there were witnesses to the gift that my father, may Allah have mercy on him, gave to my mother.

Moreover, my father, may Allah have mercy on him, was married before he married my mother, and he gave his first wife a gift of four traditional houses and two apartment buildings, which she took possession of when he was still alive. She died several years before my father, but my brothers and sisters have not agreed to this gift.

They are all married, my brothers and sisters from the first wife, and they live separately in houses that they have bought with their own money. They are well-off and they have left the traditional houses and two buildings that my father gave as a gift to their mother. They have left them and rented them out to single young people, and they take the rent for that. We – the daughters and son from the second wife – are not married and we do not have any other income from which we can eat.

My question is: my brothers and sisters from the first wife do not approve of this gift, even though they had approved of it when my father was still alive. Are gifts given to wives valid? May Allah reward you with the best reward.
Praise be to Allah.
      Firstly: 

    It is permissible for a man to give his wealth to whomever he 
    wishes during his lifetime, but he must treat wives equitably in terms of 
    giving. If he gives a house to one of them, then he must give something 
    similar to his other wife. Please see the answer to question no.
    34701 

    If he differentiates between them in terms of gift-giving, 
    but the other one agrees to that, then it is permissible, because she has 
    the right to do that. But if she does not agree to it, then he must take 
    back his gift or give the other one something equivalent to what he gave to 
    the first one. 

    What appears to be the case is that both wives agreed to and 
    gave their consent to what the husband gave, without any objection. 

    Secondly: 

    Your half-siblings through your father do not have the right 
    to take back a gift that their father gave to your mother or to anyone else, 
    whether they agreed to it when their father was still alive or not, because 
    their father has the right to dispose of his wealth however he wishes, so 
    long as that is not detrimental to the interests of the heirs. This is 
    despite the fact that his first wife, who is their mother, had also received 
    some of their father’s property as a gift, so what may be said about what 
    your mother received should also be said about the gift that he gave to his 
    other wife. So either all the gifts should be taken back and added to the 
    estate, or each should be left as it is; in fact the gifts given to their 
    mother are more problematic, because he gave her more than he gave your 
    mother, according to what is mentioned in your message. 

    However, what we say with regard to this issue is that it 
    should be referred to the courts, because it is the issue of a dispute 
    between two parties, both of which should be heard in order to establish the 
    rights and evidence of each party. 

    And Allah knows best.