You should list your thoughts and review your draft with your therapist. then, after a discussion with the therapist, send to your brother. If you pretend it had not happened, you would only see more trouble in the future coming from him; plus, you will feel awkward during the wedding. Why feel awkward if you can help it?..

In your letter to your brother, just make statements. Do not invite him to discuss. Just say what you have to say and leave it at that. If he wants to discuss, he will need to initiate a discussion.