Hi--
My great grandfather was Andrew Machusko, your great grandmother's brother. I remember him--he died in 1977 when I was 14.
As near as I can figure, there is another sister born Anna Machusko (1900-1939) who married a man named John Shimko. Their children seemed to have kept the name Shimko.
I don't know if John Shimko is related to your great grandfather, but it seems like more than a coincidence that two sisters married men with the same last name.