If he had put Sheila in the twins room, they would have known she had been moved I suppose, so in effect Sheila couldn’t have shot herself? Unless of course she shot herself once in the main bedroom and walked to the twins room.
He wouldn't move her unless she'd been in the main bedroom and he shot her there. There have been suggestions that Jeremy got her out of bed and then made her go into the main bedroom. I don't think that happened, I think she went in there by herself. That doesn't show whether it was Jeremy or Sheila who did it though. Either way, it doesn't explain why she was shot, or shot herself, in that particular place.