Sounds just like Mr. Business 5 years ago
He was a true challenge ! Wife said it was because he was a boy and a slower learner
We would take him out - he would pee , then run into the house a hundred miles an hour - run under the dinning room table and drop a duce ! Boy was my wife NOT happy with him as I was in the fall harvest mode and was not home to help her with him . Oh what memories your question here bring back
But to answer your question , at that time also was we did not let Ali and Mr. Business out together - They would get to playing ruff and He had his ears posted and didn't want to chance a problem there , I did start letting them out together and of course , Ali would do her deal and he picked up on that and started to go outside .
To me - this is a tuff call , as Mr. B would let us know he had to go outside - yet got confused on just what to do and where , I took him out on a lead and would walk him ad walk him , this just did not help with him , as he would head back under the table and poop again there , I think once they go inside it makes that much harder to correct .
I know this has not much help , but I would just keep working with him , be patient with him and he will get it .
Sorry for not much help here and best of luck