TDA, NVE, and DVDShrink will create 2 titles when combining each side. It will not be continuous. There will be a pause to go from Title 1 to Title 2. And once in Title 2, you cannot go back to last chapter of Title 1 using Prev button on, unless you add some navigation commands to do that. PgcEdit's DVDShrink macro should do the trick. With this added trick or not, you still cannot fast rewind from Title 2 to Title 1.
You can use DvdReMake Pro to combine 2 to 1 with a continuous flow, no pauses, no problem rewinding b/c there's only 1 title. Very easy. If interested, then post in DvdReMake forum. Once done, you can use CloneDVD to compress.