Incest Survivors Support Group
Incest refers to any sexual activity between closely related persons that is illegal or socially taboo. Consensual adult incest is very rare. Incest between adults and prepubescent or adolescent children is a form of child sexual abuse that has been shown to be one of the most extreme forms of childhood trauma. If you or a loved one is a survivor of incest, join the group...
I would actually try to make the talk you and mom...your older brother needs to NOT to be there if you believe he's the perpetrator.
I'm sorry I wasn't more clear... My older brother won't be present during this discussion. My mom wants a separate conversation with him another time.
Tell him you're concerned about his behaviour and that he seems to be depressed, tell him that he can talk to you if he wants to. If you or anyone else you know has benefited from seeing a therapist tell him that. Tell him you love and care for him and ask him what, if anything you can do for him. Give him space and time to respond or not.
Let him know by your actions as well as your words that he is safe with you, whatever the cause of his problems.
I think it would be a great idea for both you and your mum to talk to a therapist about this - you need to get your own ideas and situation clear before you start on his. As someone pretty well known once said 'Don't try to take the speck out of his eye before you take the log out of your own.'