Discus can be aggressive to one another if they are kept in numbers like 2s and 3s. Discus should be kept in a minimum group of 4. I've found that and even bigger group works best. Your fish are still going to develop a pecking order though. Even though your pH is a bit high if you are buying captive bred and not wild caught then you should be fine. I have an acquaintance who keeps his Discus in that same pH and has done so quite successfully for years. His fish still display great color and are just what you would expect from Discus.
BTW, if you are more than likely going to have to choose between the shrimp and the Discus. There is a good possibility that the shrimp will become a nice snack for the Discus.
BTW, if you are more than likely going to have to choose between the shrimp and the Discus. There is a good possibility that the shrimp will become a nice snack for the Discus.