I thought that on this first day of a new year I would give a bit of an update.
You were right about Budzisz. Both of my grandparents came from the same region and attended the same church in Szebnie.
I have found a bit about some cousins from New Jersey. Their grandmother Agnes was either a sister or step sister to Katherine. There was another sister Maryanna who I think came here for a while and then returned to Poland to live. There was also a brother Jacob who also lived in New Jersey.
Katherine's parents were Jacob Lybas and Veronica Kopycinski and as far as I know they stayed in Budzsiz.
Alas as far as the Mysliwy's are concerned I still Have no siblings for Peter. His Parents were John Mysliwy and Constance Kroworyk and again as far as I know they stayed in Szebnie.
How is your searching going? I hope you've had more success than I have had.