Prososki family search in Raciaz, Sierpc, Masovia, Poland 1. Open

My grandfather Bron Michael Prososki immigrated to America in 1904. He was born 9 July 1886. The son of Wladsyl Prososki (born about 1846 and died after 1945, maybe) and Julia Pychke (died before 1937).  I do not know if he had siblings. My grandfather was said to be going to medical school maybe in Warsaw or Krakow. I believe he may have attended the Cath0lic Church in Poland. Grandfather served in the US Army during World War I as corporal in The Ballon Corp from 1918 to July 1919. I know he and his father wrote letters at some point after grandfather immigrated. I never saw the letters. My Aunt, his second daughter told me about them. She may have found them after his death in 1966. I do know she had them translated to English. I would like know more about his family.