>>>They've downloaded it onto PC's and burnt it onto DVD discs
Are you sure that they've selected the option to burn a video disc, rather than a data disc? If you burn several video files to a data disc you'll end up with a disc holding lots of separate files [probably in mp4 format], plus some spare space, in the same way that copying them onto a USB stick (for example) would do. Such a disc can only be used in a computer. If a disc is to be suitable for playing in a standard DVD player it needs to contain just one file [in VCD format - but see below] that fills the whole disc.
Using decent disc burning software, such as Ashampoo Burning Studio Free, should enable you to create a VCD disc
https://www.ashampoo.com/en/usd/pde/7110/burning-software/Ashampoo-Burning-Studio-FREE
I've stated above that you should be aiming for a single VCD file which will, indeed, achieve your basic aim of creating a player-compatible DVD. However the user will only be able to play the whole video, rather than selecting particular parts of it (although, of course, he/she could use the 'fast forward' control on his/her DVD player to find something). If you want to create the type of disc that you buy with several episodes of your favourite TV show on it [with the ability to select individual episodes] you need to create a DVD-Video disc, which requires 'DVD authoring' software, such as this freebie:
http://www.dvdstyler.org/en/