Is there a sin on children if they ask their mother, who is married to a man of ill repute, to divorce him, or if they cut ties with her because she refuses to divorce him?

The fundamental principle is that marriage without a guardian (wali) is invalid and impermissible. However, if it is common in a society for this type of marriage to be considered valid, then it is ruled as valid due to the difference of opinion among scholars on this matter. Some scholars (from the Hanafi school of thought) have permitted this marriage on the condition that the woman marries a man who is her equal (kufu'). If he is not her equal, then the guardians have the right to object to the marriage.