We have a bath and a half on our top floor with two toilets and a tub with a shower in it. When flushed, the toilets will back up and then drain very slowly but not strong enough to remove the waste with it. Then they don't fill back up at all.When we take a shower, the toilets begin to bubble like crazy while the shower is draining. We have tried plunging and snaking and auger, even replacing the valves, etc. The smell is getting worse of course. We have checked the cleanout and it is fine. A year or so ago, we had some back up and had roto rooter out to check the pipe from the street to the house and it is clear also. What else can we try?

The bubbling indicates back pressure. Back pressure tels you there is a blockage in the drain line impeding the flow and setting up back pressure that sends a bubble back up the line to your toilets. The smell comes from the sewer gas that comprises the bubbles. My advice would be to snake BOTH lavatory roof vents. Put out enough cable to reach the base and 20 feet more. Good luck and let me know. Tom