Well to return to my original example and layout, the WKLB type of long barrow without the capstones would make an excellent house for the living, and the dead if it had been roofed in a more traditional way. It had what one could describe as a 'living area' and the side chambers for storage/sleeping/internment. Who's to say that the early burials were not of those that actually lived there initially or indeed later on. I would imagine that if you were still considered to be 'alive' it was no big scary thing to have dead bodies lying around in a side chamber.
Some years back now I was working at a very old thatched cottage in Hampshire where we were building a new kitchen onto the rear of the property. This meant removing the decrepid old outhouse that was already attached and where we discovered a brick lined grave beneath ground with the remains of a skellie in...headstone and all of a lady named Elizabeth. The digger driver who unearthed it fled from the scene and was never seen again!!
Burials in gardens adjacent to houses used to be very common so why not indoors as well.