If I were you I would start by interviewing every single relative you can. Take excellent notes and ask the same questions consistantly. Where ever you find these inconsistancies make a special note. Look for patterns. Don't forget to interview any family friends or neighbors who might know something. Rack your brains and try to remember all the people in your life. Do you have any clergy who your family may have confided in? Go to them for prayer and guidance and you may find some real help. Ask over and over again until you are a real nuisance. Some one will crack. Don't give up it may take years.
LM