Hi Christine - sorry to read that you're going through that.

They say you're the sum of the five people you spend the most time with. I think that applies online as well - I don't talk to many family members or IRL friends about this hobby because I'm here to have fun and be surrounded with positivity and other people who are trying to improve their craft (like everyone here on this forum!), because honestly?
The negativity they have to offer is irrelevant. Simply put, they're not experts. They don't know as much about the platform and they don't have the passion about it that we do. All they have is the common misconceptions. We all already know this is a tough thing to do, but it's not relevant to remind us of that every day because we're going to do it anyway!
They can't know how much we enjoy and believe in it until there are results that they can see for themselves, and until then, we don't need unfounded negativity. Since you can't take back other people knowing about your channel, I'd say just focus on your online friends for the online stuff - they understand it best.
And if your brother's being annoying, feel free to rant to me any time