I have not had to deal with this, so all I can do is suggest ideas.

My first thought is to discover who is doing what. If switching who is up and who is down will help with that, maybe do that "temporarily."

I don't think you want to try anything which stops them peeing where they ARE, like those counter top things, because you said right now it is porous and easy (oh, sorry, easiER) to clean up. If they are intent on not using the box and going elsewhere, making the counter top off limits could just move them to something that won't be easy to clean.

So rather than getting them to stop using what they are, you want to get them to USE what they should. Suppose you treated them like little kittens and put them in a smaller confined space with a litter box and no other options? Again, this is JUST temporary. It would be retraining them. Maybe have to do this for a week. Not sure what supplies you have and what you would need to buy to do this, but wouldn't it be cheaper in the long run than replacing rugs/counters/tables? So for a week, they would be in their kennels (or whatever small confines you come up with), one each, and maybe only let out one at a time to spend quality time with you?

Again, just thoughts, sounds like a LOT of work to me as I sit and re-read this. Sigh. Sorry I can't point you DIRECTLY to an answer!