I use DVDStyler (free front end for DVDAuthor) to make multiple audio track DVDs and it's "multiple titleset" feature (probably the same as DVD Labs multiple VTS) to mix resolutions and aspect ratios. I don't know if it can mix PAL and NTSC however. It might but the menu will be in one or the other and your DVD player might key on the menu and assume that all titles are in the menu's format.
I generally use gui4ffmpeg if I want to change the format of an mpeg file before authoring.
Just call me Steve: I never should have used numbers in a screen name, but I just can't stop now.