Enno,
The Ernst Machert I have in my family (my great-great grandfather on my mother's side) was born about 1842 and died 25 Jul 1907 in Chicago IL. His wife's name (per my great grandmother's death certificate) was Bertha Seiloff. Ernst and Bertha had at least 4 children, Mary, Anna (my great grandmother) Paul and Emma. Based upon a 1920 Census for my great grandmother Anna she was born in Keslein as were both her parents. I know nothing further on this line going back to Germany (or Poland) I've recently been in contact with another genealogist (I think you know her, Henning?)who I believe may have further information but I cannot collaborate the Ernst Machert is the same at this time.
If you can confirm you have in your family an Ernst who was married to a Bertha, and they had at least four children including a Mary (or Marie) Anna, Paul and Emma, and the whole family emmigrated to the US about 1881 or 1883 we may have a match :) I'm hoping so!
You can email me directly at alison.kozar@gmail.com and I can fill in the information on Ernst and Bertha after they arrived in the US.
Thanks,
Alison