Rescinding Surrender of Children

My question involves a child custody case from the State of: New York
The parents of 2 children surrendered their rights in court to their children. The grandparents chose to adopt the children. The adoption was due to be complete in a couple of weeks, however, the grandfather suddenly passed away. Can the mother of the children petition the court to rescind her decision to surrender the children?
The mother of the children had been on drugs. She has been clean for about 9 months now and presently lives with her parents helping to care for her children.

When did the non-parents sign the papers?