This should be pretty easy. You mentioned DVDShrink, so i will focus on that tool.
1.) For the first movie (the one where it is the only one on the DVD)--> We will call it Movie A. Open DVDShrink, and rip JUST the movie to your hard drive. Use Re-author mode, and drag only the Main Title that you want. REMEMBER where on the hard drive you are ripping this one. Do not burn it yet.
2.) For the second movie (the one where it is one of two on the DVD)--> We will call it Movie B. Open DVDShrink again, and rip JUST the one movie you wish to your hard drive. Use Re-author mode, and drag only the Main Title that you want. Choose a NEW, empty folder on your hard drive. REMEMBER where on the hard drive you are ripping this one. Do not burn it yet.
Now, pop in your new blank. Open DVDShrink again. THIS time, you are going to use the "OPEN FILES" option. Navigate to the location of the first movie (above). Just find the folder that you used, do not worry about looking for individual files. Let Shrink analyze this first movie, all over again. Then, making sure you are in Re-Author mode, click on the OPEN FILES option again. Now navigate to where Movie B is on your hard drive. In essence, you are "adding" this to the compilation. Let DVDShrink analyze this second movie.
Now, click on "BACKUP" to rip this new compliation.
This time, of course, you should let it rip this new compilation containing both movies to a THIRD location on your hard drive, and you can also choose to BURN this compilation when you are done (I do not know what program you use to burn, but you could choose Nero or DVDDecrypter, for example).
You should end up with two Main Titles. No menus. Title Two will begin playing immediately after Title One.
Hope this is what you meant.