Can an ex-spouse draw life insurance benefits?

My boyfriend's father died in August. His divorce was finalized from his ex-wife in April. Apparently, he never changed her as the beneficiary on his life insurance policy. My boyfriend and the siblings really didn't care, because they didn't have the money to begin with-so what would it matter if they didn't have it now.....however the ex-wife agreed to split the insurance money 5 ways--believing it was only fair and she had a decent relationship with all the kids/grandkids. My boyfriend and his siblings had a letter drafted by their lawyer stating that the ex-wife agrees to split the life insurance money and she signed it. It was sort of her suggestion. After all, their dad divorced her (and on a side note, his reasons for divorcing her had something to do with him pulling his retirement out early upon her suggestion so that she could place some money in an acct that would draw interest and some in the bank acct to pay bills with, only to find out that the money disappeared and she began using his credit card to pay for bills, subsequently causing my boyfriends dad to file for bankruptcy). My boyfriend got a letter in the mail yesterday from his step-mom stating she's going to be keeping all the insurance money basically because she feels entitled to it. She rattled off a list of things she has done that are only simply things a nice person would do without payment. (claims she paid his cell phone bill for a year, a gas bill in 2/08, their joint tax return in 2007, and has been feeding the cats since his death and mailing his mail to my boyfriend's sister. It's so ridiculous....however, my question is this.

Can she get away with this if she signed a notarized document stating she agreed to split the insurance money? After all, they were divorced and it was more than likely an oversight on his part. Also, would something like this be suitable for civil court and how long should it take???

Thanks all.