Apparently the US Ambassador to the UN, Samantha Power, has told US law-makers that she doesn’t know how many of the 6,000 or so deaths in Ukraine  have fallen on the rebel side – including civilians. 
This is a lie.
The US has hundreds of military advisers in Ukraine. They will have a very good idea of casualties on the side of Kiev’s military forces. Let’s say that is X. 6,000 – X gives an idea of deaths on the side of the rebels – and their families (as the question asked). 
During the illegal invasion and subsequent occupation of Iraq the US claimed that they did not have figures for the number of civilian casualties. They specifically claimed not to be counting. That was exposed as a lie by Wiki Leaks. 
(According to this web site they are playing the same game in connection with their illegal bombing in Syria )
So. We can imagine the same game is being played in Ukraine. The US will have a good idea exactly how many are dying on the side of the rebels. Including civilians. This is vital intelligence for their overall planning. But they don’t want it in the public domain because civilian deaths on the other side are not part of the published narrative about the war. (Russia is very bad and everything which is happening in Ukraine is due to “Russian aggression”).
The reality is that a few thousand dead Eastern Ukrainians are calculated as an acceptable price to pay for getting Ukraine settled 100% into the EU and the Western orbit generally. Especially considering the the East of Ukraine contains some of the most economically productive areas of