I agree...but, then, it's hardly a secret burial site. And if the families buried them, would they do it with the evidence of torture intact? The BBC reported that the first grave was of a woman who had a rope around her neck. It strikes me as odd that the family would bury her in such a fashion. Also, why would the Russians allow family members to bury their relatives with evidence of torture intact?
The whole thing just seems odd to me. The commonly-understood concept of a mass grave is of a large pit with bodies tossed in en masse. There are no grave markers and, typically, the perpetrators try to keep the location secret so their crimes go undetected.
This whole thing just feels odd to me. Hopefully, there will be procedurally-correct investigations to get to the bottom of it.
EDIT: Having read a little more, I think we're seeing multiple activities here. There was at least one mass grave that contained 20 Ukrainian soldiers. Other graves are individual, probably the deaths of civilians due to artillery or other weapons. It still seems odd that the mass grave of soldiers would be in the same place as individual family burials but it's a little clearer and more understandable now.