That's a great response to getting cut off in the middle of a sentence. I would consider bringing the topic up before it happens, if possible. It reduces the risk of someone getting defensive. What about asking them to make a silent hand gesture when they think the volume is too loud?

It sounds to me like it is not just the volume. They don't want to listen and are used to engaging in this rude behavior of just telling you to stop talking. It's become an entrenched habit. Lots of people would rather listen to themselves talk than someone else, but they only feel comfortable expressing that feeling to family members! Anyway, that's why I kind of like the idea of a hand gesture - they have to keep listening but still can express that they think your volume is too high. On the other hand, having your conversation policed at all seems wrong.

It's interesting that all three of them have their own conversational issues but instead of focusing on their own problems, they are focusing on fixing the conversational issues they perceive in you. How would they like it if their conversational foibles were repeatedly pointed out midstream? How were you supposed to learn how to have meaningful conversations if your parents and siblings model communication patterns where they don't listen to you and don't make it easy for you to follow?