Please do write to me off this site, if you would. I can answer more questions for you after that. To answer your last question first, I don't know much more about Rudolf than that he was a part of Haller's Army (Polish Blue Army), that fought in WWI with the French forces. Here are a few links about Haller's Army:
#2: I don't know any more than Tom in Chisholm about the three brothers' father Anton and his wife, other than her maiden name Avcin. I must look and see what I had for a source for that name. I think it was either a death certificate or another record.
#1: No clue about a sister or sisters for the three brothers. I suspect there were some family members that did not emigrate, for which we would need to do some more research at Stari Trg in the parish records (some day I'll return there!)
Please do contact me privately when you have a moment to write. I will see if I can find the source for the mother's maiden name again.
P.S. I'd be very interested to see a copy of the photo you mentioned in your other posting, as I am a hobby historian, and I am particularly interested in WWI since I had a soldier relative who was killed in France in 1918.