if shrink couldn't compress to a single disc then that means if you join them together the quality will probably be nearly unwatchable.
dvd decrypter will not join discs.
here's a dvd shrink trick if you run into something that cannot be compressed small enough:
use dvd shrink to compress the video as much as it will let you. this will not be small enough to fit onto a single layer dvd. instead of setting the output to burn to dvd with nero, set output to "files" on your hard drive.
after this process is co mplete, use dvd shrink to open the files that you just saved. you should now be able to re-shrink this to fit onto a single layer disc.
although I dont know why anyone would want to, but to each their own i guess
if you're still looking to join dvds, dvd2one is pretty commonly used, but I don't know much about it...