Translation:They are without us, and we are without them.
What's the sound of "z" in "bez": /z/ or /s/ and does it change depending on what follows it?
The Z in "bez" is indeed pronounced differently -- as either "z" or "s" -- depending on the initial letter(s) of the word that follows it.
At this point in my learning adventure, I couldn't possibly give you the rules for this, but I can tell you that the voiced-to-voiceless or voiceless-to-voiced change doesn't happen only with Z. (Great news, right?)