Social Security Survivor's Benefits?

My brother died in 2002. His 7 yr old daughter went to live with her great grandparents and my parents kept her every weekend and holidays. The child's mother and grandmother lived in another home and raised 3 boys (half brothers) born after my brother separated from the mother (they were never married). My niece's mom kept the checks for over 10 yrs for her household.

The great grand parents were afraid of causing problems and never spoke up. Now my niece is 20 with a four year old. They live with the surviving great grandparent. The mother said, "The child never did without", when confronted and claimed she wasn't allowed to save any money for Zoey. She said the money had to be spent.

How much could she have saved a year? Did they have any right to my niece's money? She never lived with her mother and grandmother.