DVDlabPro gots a support of Multiple VTS ... but its very complicated to get VTS Streams rigth via a VMG Menue accessed!
And some Mencoder encoded streams wont be muxed correctly!
So as in case of professional DVD authoring get MaestroDVD!! (maybe on Ebay as not sold anymore cause the rights are bought by Apple Computer) ... or Scenarist which on the other Hand is the State of art, but Looks alwfull, gots a userinterface whichs alwfull and costs a HELL!
If you just want to do easy (non multiple audio) mutliple VTS DVDs then get TmpgENc DVD Author.