Make sure you have good wax rings under your toilets-replace them, look to make sure all P-traps have water in them, third, all of your plumbing vent must be clear. Last, if a vent goes out thr roof too close to a window, the right conditions can bring gas in. Try these and let us know at [email protected]. If these do not work, we try again, I am a licenced plumber with 30 years, hope it helps.