Is it permissible for a man to request to be buried in his mother's family's cemetery, and do his maternal uncles have the right to prevent him from doing so?

There is no objection to a person requesting to be buried in a specific place, and their request should be fulfilled unless it entails hardship. If the graveyard is owned by his maternal uncles and they refuse his burial there, they have that right, and burial is not permissible without their permission. However, if it is a public graveyard endowed for all Muslims, then they do not have the right to prevent him from it. Fulfilling his request is not obligatory upon the heirs, but it is recommended as an act of kindness to the deceased.