Is it permissible to give zakat to relatives (grandmother, maternal uncle, maternal aunt), knowing their financial situation (the grandmother lives with her low-income son, the maternal uncle and aunt)? And does the ruling differ for a mother regarding giving zakat to her mother, brother, or sister?

It is permissible to give Zakat (definition) to a relative if they are among the eight categories, and they are more deserving than a non-relative, provided that they are not among those whose maintenance is obligatory upon the Zakat-giver, such as ascendants (fathers and grandfathers) and descendants (sons and grandchildren).