Two iDVD projects on one DVD??

I created 2 iDVD projects a while ago, neither very big. I now want to put both onto one DVD and have them come up when inserted into a DVD player, so the recipient can choose which one to view, and then navigate around as normal. Size is not an issue, plenty of room. I found the "project" files in my movie folder, and used Toast 8 to copy them to a DVD. Did not work. One project came up on my tv screen, but there was no way to navigate. Apparently the files are not the right type. I opened the DVD app on my Macbook, and it could not read it either. The original DVD's I made earlier played just fine on tv and on computer. So, what am I doing wrong? How do I get these two onto a DVD?

While I am at it, wondering if I need to keep the slideshows that I created to make the original projects. They are all still living in my movie folder as well. Or are they aliases that iDVD needs in order to do its thing? Would like to save the room, but may also want to (sometimes) burn the projects to give to family members.

Thanks in advance for any help!