I took a quick look at the Iowa family. Many of them are buried in the Oakdale Memorial Gardens in Davenport:
There's also a number of other family members, including "Litze Pries" born 1820 http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=pr...
; and Jochim A. Pries born 1823 http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=63...
I found an 1856 Iowa State Census for Pleasant Valley, Scott County which looks like Peter:
P.H. Pries, born 1818 in Germany, a farmer who came to Iowa c.1847
H.F. Pries, wife born c.1818 in Germany
H. Pries, male, born 1841 in Germany (your John Henry??)
Christina, born 1846 in Germany
Eliza born 1849 in Iowa
Agnes, born 1851 in Iowa
Mena, born 1853 in Iowa
The page following this had John (Joachim) and Sophia Pries who came over c. 1850. They had several people living with them, including Fritz Pries, born c.1816, who came over in 1847.
Ancestry has a genealogy for this family which has Peter born in 1818 in Kiel, Schleswig-Holstein.
On another website, Peter was the son of Litze Pries and Minna (unknown) and was born 05 Apr in Krempke, Holstein. Friedrica was the daughter of Johann Gottfried Henrich Conrad HERRING and Henrietta Graas. They immigrated in 1848 through New Orleans and took the Mississippi up to Davenport. http://roots-and-boughs.com/Kathy's%20Lines/herring.html