I have done something similar to this for an entire family. What I did was go through the stuff by myself first. This was after both of my grandparents had passed away and this was found in their things. (an entire buffet drawer full of pictures, postcards, memorablia and letters) Then when I had developed a file system based on what methods I use I put a pad of paper in each file. I listed the items in the files and questions I had about each, if any. I set about finding relatives and friends that might know what I was looking at and what it meant.
I found that doing interviews with questions in hand helped fantastically. Keeps you on track and the information flowing. I also kept a mini-recorder in the box for the interviewing of older relatives. That way I wouldn't have to interupt for the parts I didn't understand. I could trying and figure it out later or ask later.
I made b&w xeroxs of items so I could write on them when necessary for info.
I took what I had learned, started my scrapping and went back to the people I need to as I went. The letters and memorablia that needed preserving I put in vellum envelopes and such.
When I finished I scanned the album pages in color and burned to dvds. I gave everyone in the family a dvd copy. That way they had an album, plus if they wanted to spend the money to have it printed, it would be their cost, not mine. Let me know if I can answer anything else.