I dont see any reason why they would have woke up. I dont see any reason why June or the kids would have heard any commotion downstairs, if Ralf and Sheila were down in the kitchen, there bedroom doors could have been closed and the kitchen door also closed.
Looking at it from a different angle IF there was a hitman I think out of all 3 adults SC would have been the one to put up a fight, I dont think for a minute that she would have complied, and would have fought for her life and that of her kids and family.