I know that with DVDLab Pro you can make a dvd with 99 titles and each title can have 99 chapters. Each chapter can have a separate button to access it from your menu/menus, and can be played individually. This gives you a maximum of 9801 videos that can be played.
I think I might start over, and make 4 separate titles using the minidvds as the starting point. Make a chapter point for each video contained in the minidvds and put a button or image on your menu for the chapters. That would give you approx 30 or so chapters to deal with in each submenu.
I’m assuming each of the minidvds is already in dvd-video format. Lab Pro can import entire dvds, but I don’t work from disks or disk images. I’m normally importing mpeg2 elementary video and audio streams. You might have to mount your iso in a virtual drive or rip to files first.
Edit: There is a fully functional trial of DVDLab Pro—good for 30 days I think. And there are other authoring tools that can probably do this as well, like GUIforDVDAuthor, which is free.