2 Answers

Your claim to be a licensed private investigator doesn't ring true to me based on the question you've asked, the details you've provided, and the fact that you've asked it here. it really  
sounds more like you are trying to get someone to answer an essay question for you.
Viet Nam vets aren't young (your question cut off after "you") anymore.  They are in their 50's, 60's and beyond.
I fail to see why it matters who her grandpa is, that she is a VN vet, or that she is giving away alot of money.  What purpose does your investigation serve for her, your client?
Check her birth certificate; follow up by locating the birth certificates of the parents listed.  The general should be the father of her mother or father. 

If you were truly a PI, I'd fire your ass for being incompetent!