What is the ruling on a father formally allocating his house to his daughter through a sale and purchase, without the knowledge of the mother or siblings, out of fear for her being wronged by the mother and siblings after his death, in order to secure her future and education?

It is advisable to investigate the reason for the mother's favoritism among her children. If the favoritism involves financial gifts for a legitimate Sharia-compliant reason, then there is no blame. Otherwise, it is not permissible. As for her ill-treatment of the father, she should be advised gently. The mother should not be given the father's money without his consent. It is not permissible for the father to allocate a house to a daughter through a simulated sale and purchase if it is a superficial gift, because justice between children is obligatory.