I have just edited 3 home made dvds of hols and am trying to add them all into one project.
I save each edited dvd separately But now when I load project one and try to add either the saved project 2 or 3 it will not add the files. Which off course was saved from premier elements 12
What computer operating system is your Premiere Elements 12 running on? And, please update 12 to 12.1 via Help Menu/Update if you have not done that already. Are you dealing with Premiere Elements 12 for all the video involved in this issue?
Now to the core of your problem.
You cannot import a project file into another project file (Premiere Elements - any version).
You are going to have to export the Timeline content of each project into a file saved to the computer hard drive and then import the 3 files into one new project for the end product.
Just to make sure that we are in sync with your issue, is it correct that all you have now are 3 Premiere Elements 12 project files each with edited DVD-VIDEO content derived from the DVD-VIDEO format's VTS_01_1.VOB.
What is the final product going to be - NTSC DVD-VIDEO standard or widescreen on DVD disc?
What is the project settings for each of 3 projects that now house your DVD-VIDEO editings?
Looking forward to your follow up with further details and clarification.