The OP should invest some money in a lawyer who specializes in immigration law in the US, maybe he can get in touch with Rajiv's office for a consultation. IMO, I don't think there is much hope to his case of claim to US citizenship or possible a green card. Unless his 1/2 sister is willing to sponsor him, but if her mother hates his guts, the chances of a petition by the 1/2 sister is non-existent.
Forget or don't even think about his social security benefits, his wife is going to collect the minimum that Uncle Sam is going to give her. If he had a large insurance policy, his wife should be sitting in pretty good financial position.