It is just as frustrating for them as it is for you. When you look into their eyes, you can see the person that is inside but there will be that point where you can only see it as they will not be able to communicate what is there.
Goomba... it's rough brother. You are doing the right thing buy praying for him. What you need to know is that he is comfortable and not suffering with a disease that is full of physical pain or discomfort. The roles are reversed now. Treat him with the love and respect that he treated you with growing up. Be patient and strong.