Hi,

Usually migrants from Europe attended german Lutheran or Catholic churches, and I think you need to find the earliest church records which should give you the place where your relatives were born in Hannover. I have looked on this website for passenger arrivals but the earliest was 1850's
http://www.castlegarden.org/about.html

I have also looked on the UK national archive website for mention of a Fer(r)is in the British or Hannoverian army before 1850's - there are quite a few from Scotland, Ireland and England so perhaps you should visit the site yourself.

http://www.nationalarchives.gov.uk/catalogue/search.asp

I also looked to see if your family were importers/exporters which would explain why one member of your family were in Hannover - I found a Ferris grocer in Truro cornwallin yr 1810, which is by the sea, plus a Henry Feris in Liverpool so there's a possibility if only yours were English

http://www.historicaldirectories.org/hd/

Good Luck,
Rena in England