Dear Corrine: I have found that the Sosniak surname is more common than others and have found Ellis Island passenger information on my Grandfather and several of his brothers using that spelling. They all were born in Mikow/Mykiv in southeastern Poland in the years between 1872 and 1893.
I also confirmed that spelling with records obtained during a recent trip to that area.One of the brothers was named George who we have very little information on. However, he may be a lot older than your mentioned father-in-law. We lost track of him after his second trip to USA somewhere in the 1930's. I will be very happy to trade information with you if you feel your George and his parents originated from the same area in Poland.