If they don't even SMELL the smoke, they definitely are not inhaling enough of it to test positive for marijuana under any normal drug test.

It is actually quite easy to generally control the movement of the smoke throughout your house. All you need is an understanding of the pressure and normal air movement throughout your house, ie, if you have an heat vent blasting in your room, that will cause positive pressure to build up and air/smoke will be pushed into the rest of your house. Conversely, if you open a window and position a fan blowing out, that will create negative pressure in your room, resulting in all the smoke to go out the window and clean air from the house to be pulled into your room.