Sounds like you have a blockage somewhere past all those fixtures that are not draining correctly. I recently had a service call with exact same symptoms. The whole system had no vents and no clean outs. I had to pull two toilets and run my drain snake down both before I got the blockage which appeared to be right at the neck of the septic tank inlet. The customer had just had the tank pumped so we knew it was not the tank or field lines. If it were the field lines then you would possibly have water surfacing above the tank.