Is it permissible for a person to disinherit one of his children due to problems that occurred between him and his son-in-law? And is it permissible for him to give one of his children more than the others while he is alive, on the pretext that it is his money?

This will is impermissible because it contradicts Islamic law. Allah has specified the shares of inheritance in the Quran and has warned those who transgress His limits. Therefore, whoever prevents some of their children from inheriting, or gives more to others, or includes someone who is not an heir, is disobedient and sinful. Furthermore, a will made to an heir is not permissible, based on the Prophet, peace and blessings be upon him, saying: "Indeed, Allah has given every rightful person his right, so there is no will for an heir." If the apostasy of some children is proven, they do not inherit, based on his saying: "A Muslim does not inherit from a disbeliever, nor does a disbeliever inherit from a Muslim." As for giving gifts to some children over others without a legitimate Islamic reason, it is forbidden and unjust. The evidence for this is the hadith of Nu'man ibn Bashir: "Fear Allah and be just among your children." However, if the gift is for a legitimate Islamic reason, such as poverty, debt, or medical expenses, then there is no harm in it.