Over the years, we have been able to trace my husband's paternal family quite comfortably, but his maternal side is quite a mystery with no family that we have ever found.  We do have some records but are missing a big part of the picture.  I am leaving much out in the following description but this will give an idea as to the complexities involved. 
His mother, who was born in Passau, identified herself as being Jewish, but after her death, we discovered much to my husband's shock that none of this was quite reality.  When we visited the Passau archives we learnt that she was born to an unmarried Catholic woman, was baptized and her mother put down the name of a Polish Jewish man as the father.  She  married him thirteen years later but our sense is they were not together for much of that time period.  They lived in Dusseldorf and then fled to Amsterdam, living in the area the Jews were kept during WW11  (the man was sent to Westerbork but was released, a fascinating historical story)  where they both died in the 1940s.  Last year we found that they were buried in a Jewish cemetery near Amsterdam with Hebrew gravestones.  As they left Dusseldorf, they were able to send my mother-in-law to live with that man's brother and wife in the United States.  
When my husband had his DNA tested, we discovered that it was impossible for this man to be his grandfather. Not quite certain why his grandmother used this man's name as  the father, but we do have some theories.  Every person who we have looked up as being a relative have basically all come up on my husband's paternal side.  It is as if his maternal side never existed.
I know that these missing pieces of his background are weighing on him.   I was wondering if anybody has a researcher they could recommend that we could work with to find some answers in a case like this.
Thank you very much in advance for any assistance.
Anne Kestenbaum
Toronto, Canada