Real video presentations to DVD?

Here's my suggestion, tho it may be a real pain to do. I would bring the videos into AfterEffects at the size they are now. I'd convert my powerpoint stuff to just graphics in Photoshop or something similar. Change the graphics on the side when it's appropriate to the presentation in your editing process in AfterEffects. Then render the whole thing out as a single piece of video. You may have to play with the layout and Composition sizes in AfterEffects to make it balance. Once it's a single piece of video, you should be able to use your DVD authoring software to make it into the DVD.
AfterEffects and Photoshop are Adobe products. They're pretty expensive and hard to learn but that's the only way I know of doing it. There may be others, but not that I am familiar with. Premiere (another Adobe product) may be able to do something similar as well. You could try it.
Good luck. Looks like a worthy cause.