Hi Brian, I've had good luck in the past with powder carpet cleaners on my car seats. Hope that helps!
Are the seats a fabric, such as nylon, or are they vinyl?
They are fabric.
Club soda, white vinegar and Dawn will remove water stains from cloth car seats.
How do you mix them? is it 1:1 or what?
I use Murphy Oil Soap: https://chemistrycachet.com/murphy-oil-soap-uses/