Change of beneficiary

My son was at the end of a very strained and expensive 19-year marriage to a lady suffering from narcicism. She served him a "surprise" divorce package. He immediately (same day) telephoned his life insurance carrier and requested that she be removed as beneficiary of his $1 mil policy and that I $40,000) and his 3 children (remainder) be added. Children were 12, 14, and 16. A few nights later (5-7 days) his wife returned home smashed from a friend's birthday party. She ordered him from their home and suggested he return to live with his parents (6 hours away). During the night he took his life in the basement of their home while his 16-year-old son slept above and could hear the incident on August 24, 2014.. When his widow learned that she had been removed from the policy, she contested the change to USAA. USAA has appointed a guardian ad litem for the children. The "not being mentally capable" issue can be overcome with numerous witnesses who had contact with our son on the day of his death, and weeks and months leading up to that day. As far as I can ascertain, the case is still active in the Fulton County, GA, Superior Court. Where do I stand in trying to preserve my grandchildren's interests. What chance does she have to succeed.