They became orphans when Yuri was 2-3 years old That's what makes the most sense to me.

But look at pic related. If Yor is supposed to be 11-12 here because she's still 7 years older than Yuri then it just looks odd. That also brings up the question of how old was Redacted when it all went down. Was he actually supposed to be almost a teenager and this is just how Axeman draws them?

Of course maybe they're all similar ages for the cover and that's the end of it.