Air comes up down stairs toilet and splashes when I flush up stairs toilet also drain in up stairs shower air comes up and splashes water

air comes up down stairs toilet and splashes when i flush up stairs toilet also drain in up stairs shower air comes up and splashes water
You have a partial blockage downstream from the down stairs toilet.
What's happening is thar the discharge picks up speed falling down the stack it hits the partial clog and bounces back sending a bubble air ahead of it. That's what you see blowing out of your toilet.
The solution would be to pull the toilet and snake the drain line. Good luck. Tom