I'm sorry you're so stressed out over this. I hope you have at least 4 to 5 litter boxes in your home. Even though your cats go outdoors, you'll still need about one per cat plus an extra. As for the behavioral problem, this is bullying. There will always be one alpha cat and it appears your bengal has become that. Cats are very territorial so each of your cat needs their own space. Make sure you have several cat trees for them. Your bengal, in particular, loves high places, so placing shelves on the wall and creating a super highway for all your cats to enjoy can go a long way. Search "catification" in a search engine and you'll find lots of suggestions.
There are also holistic and herbal remedies that you can try. Jackson Galaxy has a line called Spirit Essences
http://www.spiritessences.comThere are remedies for almost all situations and you can see if this would calm your bengal down. People who have tried these claim they work. I have not, so I don't know, but I do trust Jackson as a cat behaviorist!
A whole other problem is that your other cats are terrified of your bengal and their confidence level is zero at this point. You're going to have build that confidence back up and bring your bengal's down just a little bit. I believe some of his behavior is just typical bengal, but the bullying goes a little too far.
Once you get to where all your cats can get along -- or at least tolerate each other -- and the bengal is not attacking any of the other cats or preventing them from using the litter box, the peeing outside the box should stop. Cats do feel anxiety and stress -- and if you're feeling the same -- they can sense this. If you take control of the situation and find solutions, I think all can live safely and comfortably in your home. A last resort would be to find your bengal a new home.