Schulitz and Torun

I am new to this list. My more than 20 year search has finally led me here.
Researching BERTHA SCHNEIDER, IDA AUGUSTA SCHNEIDER, and ARNOLD ALBERT
SCHNEIDER..Their parents were AUGUST HEINRICH SCHNEIDER and HENRIETTA DUVE. (
Bertha Schneider Gertz Heise was my paternal grandmother.)

Official records I've located indicate the above mentioned children were born
in Rudek, Torun, and Schulitz. Records located in Plock, Poland, indicate
they married and died in and around Sierpc.I cannot find birth records, and
don't know where to turn next.

August Heinrich Schneider born before 1860, died before 1881
Johan August Schneider born and died July, 1860 in Schulitz
Arnold Albert Schneider born c. 1861 near Torun, died 1881 in Agnieskowo,
Plock
Bertha Matilda Schneider born 1862 in Ruden, near Torun, married Michael
Gertz in Sierpc, 1881. Married Julius Heise of Orlowo in 1890
Ida Augusta Schneider born c. 1864 in Schulitz, married 1885 in Sierpc, Plock

Mother of the above was Henrietta Duve, dob unknown

As I consult maps it is apparent that this family journeyed from Torun region
to Plock sometime between 1864 and 1881. I have no idea if family moved with
or without the father. It came as a surprise to me when I found Russia/Poland
as the place of marriage of Bertha. Until the day she died she stoutly
claimed her Prussian heritage.

Can anyone help or offer suggestions? I'm about burned out.

Barbara Heise Grooman
Asheville, NC