Re: johann gottfried schubert 1812 Germany
comments powered by
Old Lutheran Emigration Lists have your Schubert family from Niedewitz, Kreis Züllichau in Brandenburg.
I found siblings of my ancestors by browsing familysearch records.
Records are mostly in the form of images from duplicate church books and it is a long and slow process since it's handwritten in German but names are mostly readable.
Prussia, Brandenburg and Posen, Church Book Duplicates, 1794-1874 are worth a look if that is the nearest to Züllichau.