What is the ruling of Islamic law regarding a divorced wife returning to her husband, given her family's refusal, their threat to disinherit her and harm her and her husband if the return occurs?

If you married without a guardian, following the Hanafi school of thought, the marriage contract is valid. If you wish to return to this man with a new contract, your family has no right to prevent you, for Allah Almighty says: {And when you divorce women and they have fulfilled their term, do not prevent them from remarrying their [former] husbands if they agree among themselves on an accepted basis.} If the man is suitable in his religion and your father prevents you, he would be an oppressor (ʿāḍil), and you are permitted to take the matter to the judge to marry you. You must honor your parents and try to convince them, and if they insist on preventing you, there is no sin in disobeying them while continuing to honor them.