Without a place name (or at least a region or parish), your search in Russia will be very difficult.Russia is huge now but it was even bigger before WW I.
There were 3 main settlement regions for Germans in Russia: - Volga River region (see http://www.ahsgr.orghttp://www.ahsgr.org ) - the Black Sea and Bessarabia region (see http://www.grhs.orghttp://www.grhs.org ) - the Volhynia and Russian Poland regions (see http://www.sggee.orghttp://www.sggee.org )
There were also Germans in the Baltic States as well which were under Russian rule at the time and of course others scattered throughout the huge country.
I can say with certainty that there were Hass and David families in close proximity to each other in Volhynia and in the Volga River region and there might have been one or two in the Black Sea region.
To narrow the search, you will have to do some more local research using naturalization records, church records, and/or passenger ship lists to establish at least a general location of origin other than just Russia.Another clue might be where they lived upon arrival in North America (I assume that is where you are writing from).They may have lived in a community with other folk from the same region.