RTF is a global modification that replaces all towns in the game.

Which part is the skeleton from, and why is the vampire from level 6?

The skeleton is from level 7, and the vampire is from level 6, because I'm not sure which one would be suitable for the vampire from level 7...

Added 2 minutes later
Yes, the nun is better from level 6, and the archer should also be from level 6.