Think of an ISO as an actual disc. If it's a DVD then the file structure on it gives a DVD player all the instructions needed to play the DVD plus the DVD menu (if there is one). You can't just merges two ISO's or two DVD's.
You can mount the ISO, a process that makes them appear to your computer as if they are physical DVD's and then you can copy the video files (.vob's) off them to create another project, assuming that they are not protected in any way.
Does that help?
p.s. - do you mean you want to split what is contained on your ISO up and create 3 different DVD's with the contents?
This message was edited 1 time. Last update was at Jan 31. 2018 12:01