Is it permissible for a mother and her daughter to sever ties of kinship with the paternal uncle and his wife, especially after the grandmother forced the mother to give up her daughter to be raised by the paternal uncle's wife, and the father and the paternal uncle remained silent about this injustice?

If the grandmother coerced the mother into leaving her daughter to be raised in the uncle's house, then she is an oppressor. And if the uncle adopted the girl and attributed her to himself, this is a grave evil, and this adoption must be annulled, and the girl attributed to her father. The father should have returned the girl to her mother, and if prevented, he should have referred the matter to the judiciary. As for boycotting the uncle, the general rule is that cutting ties of kinship is forbidden, unless it is for the purpose of reforming him or warding off his harm.