I hope I can tell you what I've found in a way that makes sense. One question first, your grandmother is Elizabeth. Was she married young? On the 1930 census, Joseph's family is all listed but Elizabeth, but there is a "Son-in-law" and "Wife" listed as living with the family, and I assume that would be your grandmother, Elizabeth. Do you know what her husband's first name was? It is very difficult to read on the census record.
As to how we are related, Franz (Frank) Knab is our great, great grandfather. His son William, is our great grandfather. William is your great grandfather Joseph's brother. Franz Knab and Katerina Heigel had several children. I am sure they had children named William, Joseph, and Albert. My grandfather tells me they had two other sons named John and Jacob Knab, which I assume is correct, but I am trying to find records to verify, just to be sure.
I obtained the death certificate of Franz Knab. He died on January 3, 1931 in Flourtown, Pennsylvania. He was living with his son William at the time. He died of stomach cancer. My grandfather, John Albert Knab, told me that family legend is that Franz Knab was a very strong man. (He was a blacksmith--also on his death certificate) And, he sometimes would lift trees to show his strength. He lifted one particularly large tree, leading to internal damage, and ultimately causing his stomach cancer, or so is family legend.
But, being that his son William also died of Stomach Cancer, it makes me wonder if it may have been something genetic or perhaps something due to the area they lived in, or their habits. (I know my Great Grandpa William was a chain smoker)
I learned that Franz Knab's parents names were William Knab and Eva Kubovitz, from Franz's death certificate. William and Eva Knab lived in Hungary, and that is all that was listed on the certificate. I am currently in the process of trying to obtain Katerina Heigel's death certificate to learn of her parentage, etc.
I have more information about William Knab, son of Franz Knab, and his children and grandchildren if you are interested. Let me know.
I would love to hear any info. that you have and if this corresponds with what you have found.