What computer operating system is involved with your Premiere Elements 13/13.1? What are you burning - DVD-VIDEO standard or widescreen on DVD disc or AVCHD on DVD disc?
You say that you are trying to add 2nd video and audio clip to an existing one -- what existing one -- do you mean you want to add another video audio clip to existing Timeline content in your project. If that were the case, you have the project opened and just add the second file using the project's Add Media/Files and Folder.
But, I do not think that is the whole story since you seem to be saying that you are dealing with two PREV files. PREV does not fit into any scenario that I can think of. So, we are going to need more details.
Once you add media to a project, their fate is
a. Save the project with its Timeline content, resulting in a .prel file saved to the computer hard drive
b. Export your Timeline content to a file or burn to disc....this file or burn to is then independent of the project file (.prel) from which it was produced.
Now if you created a new project file for each of video 1 and video 2, you will have two different project filed (prel). And, you cannot import one project file into another.
Please clarify what you have done and then we give you suggested procedures for what you want to do.
Any questions or need clarifications on the questions, please do not hesitate to ask.
Add On...which should have begun my post numbered one...
I thought that I was reading your Premiere Elements 13/13.1 question in the Adobe Premiere Elements Forum.
After I posted the reply, I see that your thread is displaying in the Adobe Photoshop Elements Forum.
I am not sure what is going on with the location of your thread. But, from your problem details (Elements 13 and video), your thread should be posted in the Adobe Premiere Elements Forum.
We will try to keep track of our replies in spite of the thread location. Hopefully a moderator will straighten out your thread location.
Now I notice that your thread is displaying in both the Adobe Photoshop Elements Forum and the Adobe Premiere Elements Forum.