Is it permissible to give Zakat al-Mal on behalf of a deceased father, with the intention of it being an ongoing charity (Sadaqah Jariyah), knowing that the father used to pay this money to specific poor people he knew?

It is permissible to give charity on behalf of another, whether it is an ongoing charity (Sadaqa Jariya), such as endowing assets, or a non-continuous one, such as giving money to the poor. Both are good deeds. The hadiths confirm that the reward for charity reaches the deceased, benefiting both them and the giver. Zakat must be given from one's wealth with the intention of it being Zakat, not charity. Thereafter, it is recommended to give charity on behalf of one's father. It is also advisable to give Zakat and charity to those whom your father used to give Zakat to, in order to maintain kinship ties and ensure continuous prayers.