How to copy two DVD files into one DVD.

I want to copy the videos from 2 mini DVD into one single 4.7 video DVD.

I’ve all the files copied from 2 mini DVDs.
Each of the mini DVD contains 5 files of type .BUF, .IFO and .VOB.

I’ve nero 6.3.

When I use the Nero DVD Video, It does not allow me to add the files from 2nd mini DVD because their files names are same as first one.
If I rename just the vob files and try to add then while burning it says 'DVD video files complainace failed'.

Is there is any way to recreate .ifo and .buf files for new renamed .vob files?

All I want is to copy the files from 3 mini DVDs into a single 4.7 GB DVD and make a Video DVD.