Thank you for all your help. I have now been able to rule out this family as my John Henry Peter Pries'.
They did have a son Henry a couple of years younger than my John Henry.
Their Henry is on the census records and he is buried in the same plot as his parents Peter and Friederika Pries. My John HP Pries is buried in Sydney.
Peter's probate menitions 4 daughters and 2 sons Henry and Adolph. The daughters are Christina, Eliza, Agnes and Mena.
I'm now wondering if John HP left Germany in 1867 bound for Australia via the San Francisco port without his family. That would account for him not being on any census records. Maybe his sisters immigrated to the US as adults too.
*sigh* He's a hard nut to crack!
Thanks again and happy researchng :)