Is it permissible to marry with a valid Sharia contract, fully documented, without a guardian (wali), and with the knowledge of a small number of close relatives, given the parents' refusal and the former husband's threats?

A Muslim woman is not permitted to marry without a wali (guardian). If the wali prevents his ward from marrying a suitable man whom she has accepted, his guardianship is forfeited and transfers to the next closest guardian in line (such as the brother, then the paternal uncle). If all of them refuse, she is permitted to marry herself out of necessity, and this is the view of Abu Hanifa. It is not a condition to publicize the marriage to all people; rather, it is sufficient to announce it among close relatives.

Despite the legal ruling, we do not advise you to marry this man, because this marriage is fraught with many problems from your family, his family, and your ex-husband, and it may be difficult for it to continue under these circumstances.