What you are talking about is not particularly easy, especially if these are now in dvd-video form. Mpeg2 that is found in dvds is not a good format for editing/enhancing. It would mean reencoding the video using filters, probably using AviSynth scripts and a good encoder like HCenc. Then authoring again to dvd format.
I understand that Womble MPEG Video Wizard DVD has the ability to apply filters to mpeg2. I don’t use the program and haven’t tried this, but it is an option for you. You might be able to apply some basic sharpening and noise reduction filters with this program. There is a 30 day trial of the program if you want to test if it will help with these dvds of yours.
I also strongly advise going to www.videohelp.com and posting your question on their forum.