Is it permissible for a wealthy man to give his Zakat to his daughter's poor son, or to his daughter who is married to a poor man, or to his poor grandmother, and what is the evidence for that?

It is not permissible to give zakat to grandparents and grandchildren according to the majority of scholars, and this is the most preponderant opinion. They justified this by stating that these individuals are considered part of the zakat payer's direct lineage, and their kinship resembles that of an heir. As for giving zakat to a poor married daughter, please refer to Fatwa No. 99619.