What you report is what it is.
Each burn to of Timeline content to DVD-VIDEO format on DVD disc results in the disc containing one OpenDVD Folder and one VIDEO_TS Folder.
Only one VIDEO_TS Folder can be put on a DVD-VIDEO disc even when Premiere Elements is not involved. I have seen that written about online, and I have
never found a way to overcome what seems to be basic behavior description of DVD-VIDEO..
Premiere Elements will allow you to write to a disc with content already on it, but only after you give the OK for erasing the disc content before going ahead
with the burn to.
If you have several movies, one possibility is to build a Timeline with the movies, use stop markers, and setup disc menus according so that the viewer
can selectively watch the movies. More on that later if wanted.
Any questions or need clarification, please ask.