How do I burn multiple Ubuntu isos on one DVD?
I don't know if it can be done from within Ubuntu ( that I know of), but you can use MagicISO. The only problem it is Windows based. If you have access to a windows machine, it, you can take a look at it.
MagicISO has ability to create Multi-Bootable CD/DVD image file so that the user can incorporate multiple installation CD into one CD/DVD, and install multiple Operation System from one CD/DVD.1
1Source: MagicISO
Even though there's already an accepted answer i'll add this solution as well for the sake of completeness. And also coz' this answer better describes what's happening 'under the hood', so to speak. Creating Multi-Boot Discs.