Is it permissible to demand the demolition of the new graves built upon old graves and the removal of the rubble without harming the deceased, and what is the ruling if those responsible refuse to do so?

Building upon graves is forbidden. The deceased is harmed by building upon his grave, not by its demolition. What is prescribed is the demolition of whatever has been built upon old graves, due to the saying of the Messenger of Allah, peace and blessings be upon him: "Nor any elevated grave but you level it." It is not necessary to remove the sand. If the person who built upon it refuses to demolish it, then it is best to refer the matter to scholars and involve righteous people for mediation.