Is it permissible for a mother to donate a quarter of her house to her deceased son's children, and divide the remainder equally among her daughters, knowing that she has other sons, and is there any injustice to them in that?

The obligation to equalize in giving and the prohibition of favoring applies to children of the same degree, and grandchildren are not included in this. Therefore, there is no harm in singling out the sons of the son with some money. If the questioner intends a will after death, it is not valid for an heir, according to the Prophet, peace and blessings be upon him: "No will for an heir," and the sons of the son here are heirs. However, if she intends a gift during her lifetime by transferring ownership of the house to them, there is no harm in that, as she will be equalizing between her two daughters. For someone who passes away leaving two daughters and two sons of a deceased son, the two daughters receive two-thirds, and the two sons of the son receive the remainder by ta'seeb (residuary inheritance). Matters of inheritance should be referred to the Sharia courts to verify them and ensure the rights of the living and the dead.