I don't know why you seem to think that a court appointed lawyer is inherently bad. Court appointed lawyers have a great deal of experience in criminal defense, and therefore in many cases are excellent criminal defenders. Pro-bono representation on a criminal matter will be very difficult to find. A case such as you describe would be very time intensive, and remember, lawyers are in business to make money.
You might be better of by speaking with his court appointed lawyers, and asking him/her to explain the case, and what he/she is doing for your brother. If you don't understand the explanation, then ask questions until you do.
Now.. depending on the state that you are in, if he is not competent to stand trial, then he will be held in a secure mental health facility until he is competent enough to stand trial. Some states allow an insanity defense. Some do not. Even states that allow an insanity defense usually have restrictions on it and you need to understand that mentally ill does not necessarily mean that he escapes responsibility for crimes committed.
You can contact your local or state bar association and ask them for a referral to any criminal defense attorneys who do pro-bono work.. but it will be a short list.
Advice: You are seriously ill. Get rid of the guns and seek counseling.