Father passed and didn't leave anyone on his will for one of his accounts

Hi. My father passed away in June 2014. He was married, to my mother, who passed away also in 2004. My father remarried but about a year-2 years before he died he and his wife were not together (restraining orders, living in different states, took her off medical insurance). He left a partial will basically and didn't put everything in it. On his death certificate (he lived in NY, kids and ex wife live in MA) it says "married but legally separated". There is one account he left to his mom, who also passed away last year, and the question is, who has the rights to this money?