Assuming I am old enough to be either your mother or grandmother may I make a suggestion? Talk to them before it's too late. Leaving home at twenty meant that I lost some "adult kid" time with my folks and now regret not asking them enough questions about their early lives. After a conversation with one of my kids who said "I didn't know that" about three or four times I decided to rectify the situation.
Starting in early September I had a sticky note pad in every room in the house and when I thought of something to share, wrote it down. After a month's collection put all the notes in chronological order, transferred to a legal pad (had about two pages) and started to write. Interestingly enough as I was writing related stories occurred to me and it really went fast. I called on a 90 year old cousin to help fill in the blanks and by December 1 it was pretty well wrapped up.
The last few days have been proofreading and formatting and Monday morning I will deliver it to the printer. I had no goal but here it is in time for Christmas. As it turns out I probably enjoyed the process much more than the kids will in reading it, but I've told them they have to read it, there will be a quiz, and then they can put it on a shelf forever. I've now done my duty.
I recommend the exercise and hope that you can either convince your parents to start the project or if not, start by doing interviews yourselves. I can almost guarantee you won't be sorry.
Have a good weekend--
ps-if you're my age, as my husband told me when I started, "You'd better hurry up."