Johann Wuestmann died on 1 April 1882 in Kings County, Death Cert. Nr. 3924
Elizabeth Wuestmann died on 16 Dec 1900 in Kings County, Death Cert. Nr. 22687
I would order both of these. Next, I would look for their obituaries in both German and
English newspapers. They lived at 242 McDougall Street in Brooklyn.
Hopefully, the obituaries will note the church from which the deceased were buried and
what religion. I would then contact them and ask for their burial records in the hopes of
finding a clue to their parents or places of origin. Also, check the cemeteries too for a
family plot and others who may be buried on it and their relation.
You need to go back and search the censuses again - I found this family in both the regular
Federal and New York State cenuses under Wuestmann, Wiestman, Westman, Wustman, and Wuestman. All seem to reference either Germany or Byron (a phonetic attempt at the German name for Bavaria).
In the 1900 census, Elizabeth notes immigrating in 1847 and that she was born on Dec 1, 1820.
They were the parents of:
Margaretha * 1848 oo Scheidecker
Maria Margaretha * 1850/51 oo Anton Ebel
George * 1853 oo Helena or Lena
Elizabeth * 1860
Joseph * 1865
John * 7 Jan 1872
Johann was a shoemaker. In the 1875 New York State Census there was a John Miller
living next to them - possible brother or cousin to Elizabeth?
I think your best bet is to find and search the church records (burial and all baptismal records for all the children in hopes of learning about other family members located in New York and whose origins may provide a link back to Germany), both his and her wills and probate records which may hopefully list family members back in Germany, obits in both the German and English newspapers in New York, etc.
Good luck - lots of great opportunities.