Is it permissible to give an ongoing charity from the deceased father's monthly salary, which is designated for the heirs (mother, sister, and brother), on behalf of the father and his mother?

Righteousness towards parents is among the most noble acts of piety. Part of being righteous to them is to continue being righteous to them after their death, based on the Prophet's (peace be upon him) saying: "When a person dies, all his deeds cease except for three: a continuous charity, or knowledge from which others benefit, or a righteous child who supplicates for him." Continuous charity is waqf (endowment).

If a child gives charity on behalf of their father or mother after their death, its reward reaches them by the grace of Allah, based on the hadith (definition) narrated by Aisha (may Allah be pleased with her) that a man said to the Prophet (peace be upon him): "Indeed, my mother died suddenly, and I think that if she had spoken, she would have given charity. Will she have a reward if I give charity on her behalf?" He said: "Yes." This is by consensus.

The monthly salary disbursed after your father's death to your mother, brother, and sister is their money, and it is no longer your father's money. Therefore, it is not permissible to dispose of it except with the permission of the beneficiaries, based on the Prophet's (peace be upon him) saying: "Indeed, his money is what he sent forth, and his heir's money is what he left behind."