Since you didn't list the Stefan's parents' names I'm assuming you are looking for them.
If you haven't already I suggest getting Stefan's obituary and death certificate. Check with the Genealogical Research Society of Northeast Pennsylvania in Olyphant, PA for the obit. The PA Div. of Vital Records would have his death certificate if he died in Pennsylvania. Both might list his parents and the obit might list siblings.
If that doesn't pan out try to get the same for any of his siblings you know of. One of them is bound to have the info.
You might also try to get the marriage records for the two brothers as they might have info on parents. The are probably on record at the Lackawanna County Register of Wills office.