I would think that they would be alright, but if not they should be able to play it in the computer (if they have one) without any problems.
Can you ask what dvd model they have and look up what it is capable of playing? I want to dvdrhelp.com used to have a breakdown of what machine played what format (PAL, NTSC, -R, +R).
It's been a while since I read up on the whole PAL/NTSC thing. I know there are region-free players, we actually have one. Usually the cheapest dvd players are the ones that play anything. I think we have a cyberhome one that I can play PAL on without a problem (and just about anything else I throw at it too!).
EDIT: I just looked at our videos. They are in .avi format. Did you convert them? If not, you need to find out if their player can handle .avi's.