You don't need to write any script for merging just 3 projects once into a new project. The *.prj files are text files which of course can be also opened in UltraEdit and edited there.

For each of the existing projects

• open the project in UltraEdit,
• open File Tree View if not already opened,
• select tab Project if not already selected,
• click with secondary mouse button (right button) on project name at top of the list,
• click with primary mouse button (left button) on context menu item Edit Project File,
• select all respectively select the sections you want merged in a new project file,
• copy those sections into a new *.prj file.

I think the sections are self explaining. It should be no problem for you to understand the data and copy the project data right into a new project file. Once the new project is created completely, open this new project with merged data.