iDVD is used for burning movies to disc. It sounds like by the term "streamline" that your intent is to edit them. For that, you would use iMovie.
How you import them into iMovie depends on what format you dubbed the VHS tapes to. iMovie can be used for this purpose, so I'm guessing you chose to use a different piece of software for this. Can you tell us about what format the footage files are in, and how you came to convert them to digital?
Aha. So, you literally copied them from a VHS to a recordable DVD set top box. So, in essence, you will need to "rip" or convert the data from the DVDs into a format that iMovie can understand.
Here's an article that should help, just ignore the final step about exporting to FaceBook:
From DVD to iMovie to Facebook | Macworld