[Ger-Poland-Volhynia] German first and last names

[Michael & Maureen McHenry]

I will be looking for marriage and births on some FHL films. The only
record I have of my grandfathers parents are Americanized

John Muller
Mary Ann Rook

I had some suggestions for Rook= Rukke or Wruk. Also John =Johann. The
translator on the SGGEE site doesn't give a result for Mary Ann. Does
anyone have some suggestions?

                                 Mike