Hello, my name is Ketsha, i am 15 years old and i have had these same symptoms for about 4 years now. I honestly believe that there could be 3 possible causes to these unexpected things that happen.
1. You're child could have an amazing imagination that might have added up to imaginary people, because he is still pretty young.
2.Yes a medical illness could be a possibility, such as schizophrenia, but, because your child is this young, it is highly rare.
3. There is a possibility that what is happening is real, and deals with something spiritual, something that medical professionals refuse to acknowledge.
Ask your baby if the people he sees are real. A child knows the diffrence. tell him to draw them. write down what they say. things can seem unusual. You're his mother. You will know what to do.
A little tip for you, ask him if the voices are inside his head or outside his head? If he doesn't understand this ask if when he hears it is it like when he talks with you? If the answer is he is unsure or it's like when he talks with you , take him to a child psychiatrist along with your other son. Yes you are right it is not a symptom of ADD or ADHD. It can be a fine line with children and it is often related to a psychotic illness or extreme levels of anxiety or depression. I am not sure what other symptoms he may have as you have only mentioned a few. Yes you need to consider the childs imagination but this little tip will help determine the possible cause. Failing all it won't hurt to see someone for help.
I know hearing voices is a symptom of schizophrenia, and I have heard of it being passed down or running in families. I would consider taking him to a psychologist. I took my middle son when he had self esteem/ school issues and my youngest to help with seperation anxiety. It never hurts, and can also help with other areas of his life he might need someone to talk to about.
Did any of this start after watching a scary movie or reading a scary book? Maybe his imagination is getting the best of him. My youngest is 12, and still gets really freaked out with horror movies.
Hearing voices is not a symptom of ADHD or ADD. It is a symptom of some other mental problems, however.
The fact that he hears voices, can see people who are not there, and that his brother has the same symptoms means that you should have both children evaluated by a psychiatrist as soon as possible.