How do I sync video and peoples reaction to it

[bmklawt]

I just finished putting all my mothers films on DVD, (Workprinter XP)
The whole family will be together next week, I would like to show the DVD’s and video record the family’s conversations and reactions to the DVD and then add the audio to the DVD. If possible also add the new video as a “picture in picture” maybe.

How do I record the family and then sync it up with the DVD?

Is there some way to do this, all I can think of is to have a TV or mirror in the background.

I don't know if matters but I will be recording the reactions with either a Sony DCR-HC40 or a Sony Vx3

Your help is greatly appreciated,
Bruce