Can estate executor manage SS kids benefits, instead of the father?

I've been named executor of my cousin, Mary's, estate. She passed at 38 yr old. She is survived by her 3 kids (19, 9, and 7 yr old) and husband. They remained married for the kids. Mary was the sole provider. Husband had 2 other kids by other women during his marriage to Mary. Her husband has had a history of greed and even thru Mary's illness she knew he was unfaithful. Prior to her passing, Mary put together a will for all assets to go to her kids and explicitly stated her husband is to be excluded from her will/estate. She also had the husband sign a post nuptial agreement excluding him, and he agrees to not contest. Mary was receiving her social security benefits, since she was out on long term disability due to Cancer. After her death, her husband started receiving the SS checks, in the kid's behalf. As executor and manager of kid's trust, is their any legal avenue I can take to make sure SS benefits are protected from husband and managed by assigned estate executor instead?