I know someone named Davidovici, pronounced /dəˈvɪɾəvɪtʃ/ (i.e., rhyming with witch. It's from Romanian). How is it pluralized (as, to refer to the family): Davidovicis or Davidovicies?
The Chicago Manual of Style recommends that when a plural form suggests a false pronunciation, the name is best left unpluralized. (Preferably this would be done by recasting the sentence to avoid the need for pluralization.) Since "Davidovicies" looks like it would naturally be pronounced with "-eez" instead of "-ez", I would recommend avoiding that particular form no matter what. If you must pluralize it, simply adding the 's' looks like the best thing to do.
Davidovicis. Proper names are best treated as slightly less mutable than other nouns when pluralizing. For example, for a family named Perry, one would write "the Perrys", not "the Perries".
The bind you're in is basically one of a poor match between spelling and pronunciation. If the name had been Anglicized as Davidovitch, we would pluralize it as Davidovitches and all would be well. Appending -es is basically trying to pluralize as if that were the case. Trying to apply a spoken pluralization to a written word when the written word already doesn't match its pronunciation is pretty much just piling breakage on breakage, though. Stick with pluralizing the written version based on its written form and the spoken version based on its spoken form.