My ex-husband just passed away and we discovered that his be

My ex-husband just passed away and we discovered his beneficiary was changed from our two daughters to a woman friend he hadn't seen in five years. If we can find her, what document do we have her sign over the money to his girls? If she refuses, how do we stop her from putting in a claim. My ex wouldn't have ever changed beneficiaries in his right mind. He had a long history of drug use and we suspect this woman took advantage of that or forged his signature.
What do we do? We had to beg and borrow to bury him as we had no access to his policy that (by the way) I paid on during our marriage and even afterward our separation.