I want to connect one outdoor stove and one grill to the gas line in my backyard . Could I put the Y connector after the gas regulator?
The gas regulator is keeping your appliances safe from the relatively high gas transmission pressures. The only risk is that the regulator is set for one appliance and adding another one with the Y connector causes a pressure drop so that neither of them work. But if you are not going to use both at the same time, that may not matter.