Help me rescue our outside chairs

[absolutelyknackeredcow]

We bought new outside sofa and cushions - and stupidly - the cushions aren't washable.
It wasn't a cheap set but on the first outside visit a friends bloody Dog put dirty marks all over it and my friends child dripped grease over it I looked online and it said wash them with dilute washing detergent which I did and now I have massive water stains and the stains are still remaining. I'm so frustrated
Any suggestions?

What are they made of? Are they removable?

Put them in rhe bath give them a good scrub, then leave to dry.

Not sure what they are made off but you can take them off

I don't know if this will work but my car chairs are light grey and even rain water stains them, car upholstery cleaner might work.