What form are the old ones in? If they are in an iDVD project file there's no way to view them without going back to High Sierra so iDVD will work.
iDVD project files just reference the original source files that are in the project. They could be photos or movie/video files located in iPhoto or iMovie.
If you want to create video DVDs go to the App Store and search for "video DVD". You'll find a number of potential candidates for authoring video DVDs and burning them to disc. Most have a demo version for free to try before purchasing. Be warned that none are as intuitive or powerful as iDVD was.