in the bridge district, there is a house right next to some bridge-like thing that has some hostile characters with weird names inside. Why are they there? Inside there are some scrolls and gems.

Who knows? Perhaps they were intended to be part of a quest plot, but like several other ideas, they never finished this one. Now it's just a pretty tough fight for some good experience. ;)

is one a beholder???? well who cares anyways kill them all and let the gods sort them out

You mean these 3-4 guys, from whom one will summon some demon thingie? Yeah, beats me why they are there, but they certainly are not that tough. But fun it is and who am I to say no to extra XP and free cash heheh..