You might be interested in getting a book such as one of these to also give to your respective parents:
The Book Of Me
Memories for My Grandchild
A Mother's Legacy
These workbooks ask questions intended to remind a person who is writing their life story of things that they haven't thought about in a long time but want to include. I don't think I would actually use one of the books. There isn't enough room in the spaces to write all that you might want to say about one topic then there are other questions that don't apply and so the space is wasted. The questions aren't always in an order that you want to write in either. It is a very good way to jog the memory though.