P£OSZAJ - from the płoszyć (to scare up), possibly a nickname given to a hunt beater who hit tree trunks with a stick and rustled bushes to scare out any game for the squire to take pot shots at. Or a toponymic nickname from Płoszów or Płoszyce (Frightville, Scareboro).
BIELAŃSKI - Bielański means a resident of Bielany. That locality's name might be translated as Whiteville, Whitmont, etc.
STEFAN - popular Polish Christian name from Greek Stephanos meaning garland or crown.
IRENA - popular Polish Christian name from Greek goddess of peace, Eirene.
DUMANOWSKI - root from dumać (to ponder, think, ruminate, consider). There is a locality in Croatia called Duman which would be the perfect toponymic soruce. Dumanovksy is known in other Slavonic lands as well.