I believe the blood in the kitchen can only be Nevill's, due to the improbability of blood transference.
I do not see how the blood in the kitchen could be June's, given the evidence we have in the master bedroom.
The blood need not be Sheila's, even if she is the killer, and we currently have no expert findings that she was injured in a struggle. Furthermore, had Nevill struggled with her in that manner in the kitchen, it seems to me doubtful that she would have committed the massacre. Nevill would have overcome her. The theory that Sheila is the killer rests on Nevill not making that attempt and Sheila not having been injured prior to shooting herself or being shot - which, again, is consistent with the evidence, whether the killer is Jeremy or Sheila.
While Adam is certainly a troll, it has to be acknowledged that a lot of what he says is correct.