When I run water in the kitchen sink air comes out the stool in the bathroom.

Bubbles indicate a partial blockage dowmstream from The toilet. This can be snaked either from the bathroom roof vent or take up the toilet and snake from there. If you're snaking from the roof vent put out enough cable to reach the base and 20 feet more. If you're going to pull the stool put out 20 feet of snake. Good luck and thank you for rating my reply. Tom,