I'm not saying fraud won't happen, but have you ever considered your story the other way around. Let me rewrite your story to let you know what I mean.
A man and woman get married and have a daugher. The man gets a retirement check in his old age. then the wife dies.
To keep the retirement money flowing in the daughter convinces his pop to "marry" him with a wedding. Father and daughter live now as man and "wife'. Then Father dies and daughter continues to live on Poppa's retirement check as the "spouse".
If daughter gets another "spouse" and the daughter dies can the new "spouse" continue to live on Papa's retirement check?