> As far as I know history, but I may be wrong, Lužički Srbi are also known
> as "Prusi" or Prussians!?

You are very wrong. Prussians were Baltic tribes living in what is now 
north-eastern Poland. They were either exterminated or germanized by German 
Teutonic Knights in 13th to 15th century. As far as I know no traces of their 
language remained.

Sorbians are a Western-Slavic community still living around Bautzen and 
Cottbus in Germany. No connection at all between the two.

Marcin