Your brother will not likely ever truly get it. Few do. You need to find your comfort zone with relationships, conversations, etc. I know that the most important need I have with visual and auditory limits is the ability to have some level of control of my environment and time in that environment. If I sense I am hitting my limit, I need to be free to leave that environment.

Your past social network may not be the one for your future. Maintaining family contacts is still important. Finding a way to maintain communications with family is important. I struggled to talk with my 90 year old mother. Too much degraded transmission with wireless at both ends meant I needed to use a hardwired landline. It may make calls easier for you.

A concept to consider is simple. The dysfunctional auditory processing system often becomes limited in its ability to process complex sounds. Poor transmission, background sounds and voices, accents, and other auditory stimuli end up being chaos to us. If we can reduce or remove these conflicts, we can do better.

A prime example is calling customer service. If I get India or the Philippines, I have a strong accent and VOIP sounds to sort through before I can even begin to understand the sentences spoken. As I say, getting the Philippines is like talking to SpongeBob under the Sea. I ask for a domestic call center. It is worth the wait on hold because I can effectively communicate and resolve the need for the call. If I try to continue with India or the Philippines, it will take longer to resolve the need than the combined wait on hold and discussion.

For this reason, I try to avoid important calls with smart phones and speaker phones.

The same goes for conversations with groups.

It may help for you to get a better understanding of where you function best so you can try to tell your brother more. You seem to get very specific about anatomy and physiology. Rather than trying to identify the root cause, applying the same to understand the specifics of where you work best so you can moderate your life with targeted action will likely benefit you.

I am not hesitant to say, "Hold for a moment. I need to close a door so I can focus on our conversation."

Or, "Can you take the call off speaker so I can hear you better ?"

And, if your brother does not get it, don't let it get to you. It is your life.