Hi Len
Not too excited by these,

but:
VOLCKMANN, Chr. age 48, to USA in 1857
Chr. age 61 to USA in 1882
C. age 32 to USA in 1854
no matches for VOLCKMAND
no matches for FOLKMAND
VOLCKMANN, C, born 1827, arrived NY in Oct 1851.
VOLKMANN, C, born 1829, to USA in 1851.
FOLKMANN, Carl, age 19, to USA in 1856.
All were male, most born Germany. Did not find any reference to Wilhelmina/Helene DECKER or married name, nor to Mary/Minnie.
If any of the above, are of interest, I can provide some more detail.
Valerie