Hello Lawrence
You mention that Maurice Exiner's father married your grandfather's sister.
We are the Australian branch of the Exiner family. We are descended from Leopold Exiner (my great grandfather) who was born in Posen (then Germany, now Poland) in 1845 and died in Berlin in 1908. Our family legend is that Leopold had a brother who emigrated to the USA in the 19th Century. But noone knows what his name was.
Today I discovered, on this site, a Moritz Exiner who emigrated from Posen in 1857, aged 23.
Do you have any more information about Maurice's father? Given the similarity of the names, I am wondering whether this Moritz may have been Maurice's grandfather (or even father though he would have been in his 60s).
I hope I will hear from you.
Best wishes
Ron Exiner