I have back to back toilets and when I fluch one the other toilet empties. Would you know a reason to why this is happening?

I have back to back toilets and when I fluch one the other toilet empties. Would you know a reason to why this is happening? Sure sounds like a blocked vent, Let me explain. When you flush the discharge sets up a vacume that's relieved by the vent,
If it's blocked the suction attempts to relieve itself through the other toilets trap pulling water out of the bowl.
The solution would be to snake the roof vent. Put out enough snake to reach the base and 15 more feet. Good luck, tom

Thank you tom.