The Hempels of (possibly) Osterode District

Greetings. I've just begun to research my German
ancestry, and have determined (through census data
from the later 19th century) that my 3rd
great-grandparents Charles Hempel (b abt 1822/23) and
Augusta Klapperodt (b abt 1827) as well as their three
sons (Charles, John, and Ernest) seem to have come
from the Kingdom of Hanover (in present-day Lower
Saxony).

I've contacted a research unit at the University of
Hanover that specializes in Lower Saxony ancestry, but
in the meantime I'm wondering if anyone might speak
German, and be willing to do a lookup in the
apparently free archives linked by this research
service. My German is extremely primitive, and my
attempts to use online translators have been rather
dismal failures. I have little idea what if any
pertinent information might be available in these
archives, but I thought it was worth a try.

Here is everything I know about the Hempels so far:

The Hempels arrived about 1865, and settled in Norfolk
County, Massachusetts. They told census takers in 1870
that they came from Hanover (by which I presume they
meant not the city but Kingdom of Hanover), and
Charles Hempel Sr or his wife Augusta told 1880 census
takers they were from Prussia (which is consistent,
given that Hanover was invaded, and occupied by
Prussia in 1866).

In the 1880 census Charles Hempel Jr told census
takers he was from "Osterow, Germany." There is no
such place as Osterow, Germany, but there is an
Osterode am Harz in Lower Saxony, which happens to be
a few miles from Augusta Klapperodt's possible place
of birth - Herzberg am Harz (this according to her
cemetery record - at least there Herzberg part [there
are multiple Herzbergs in the country but this is as I
understand it the only one in Lower Saxony]).

According to census recrods, Charles Hempel (Sr) (who
may have been named Carl [if not Carl Augustus]
Hempel) was born in 1822/23. Again: we don't know
where in Germany he was born but Osterode am Harz and
Herzberg am Harz are possibilities. He married Augusta
Klapperodt (and this may be only an approximate
spelling) - perhaps sometime in the mid to late 1840s.
Augusta was born about 1828 - again, perhaps in
Herzberg am Harz.

Charles and Augusta's first son Charles William (who
was likely named Carl Willhelm Hempel at birth) was
born in 1850 (perhaps in Osterode am Harz or
thereabouts). Their second son John (perhaps named
Johann) was born in 1856 in Germany.Their third son
Ernest L Hempel was born in 1864, also in Germany.

The Hempels were jewelers by trade, and there has been
some speculation in the family that they might have
been Jewish converts to Christianity before coming to
America. We have no hard evidence to support this
possibility, but the circumstantial case is not
without merit.

The archive is located here:

http://www.staatsarchive.niedersachsen.de:80/master/C504_L20_D0.html

Any other tips or leads that you think may be helpful
would be welcome.

Thank you very much.

Best regards,

Kenneth