Hi tigces
Why dont you go and see them , and talk to them, I certainly wouldnt put a cassette tape in an envelope with a note saying tell me your life story. You will find you may get more info by talking to them and taking notes. I know my elders dont mind talking about their past, and families. Tell them you are trying to trace your family tree, you may be surprised how interested they might be. The only prob is if you live in different countries, but then there is always the phone.
Other people might do it different, but I have had no probs with my aunts and uncles, who have devulged a lot of family info
good luck with which ever way you go
regards
ricky