What is the ruling on cutting off ties of kinship with an aunt who practices sorcery, knowing that her children still maintain a relationship with their father?

Treat your aunt with kindness and forgive her injustice, for these are characteristics of the pious. Try to reconcile with her through messages or calls, as that will remove what is in her heart. You are the gainers by being good to her, whether she responds or not, and she is bound to respond. The Prophet, peace and blessings be upon him, said to one who maintained ties with his relatives while they cut him off: "If you are as you say, then it is as if you are feeding them hot ashes, and you will continue to have a supporter from Allah against them as long as you remain in that state." So repel [evil] with that which is better.