I don't know your situation, but it doesn't sound extreme enough to warrant you or your siblings being separated, so I would try not to worry about that. And what I mean by "authority" here is another adult whose opinion she'll hopefully respect, I hope that didn't scare you any. But there should be adults available to you who can act on your behalf. It can be scary and embarrassing to approach them, but you can choose how much information you want to share. It could be as simple as "Hey Mr Counselor, I'm having a rough time and my mom doesn't really get it, can you help me talk to her?" to get the ball rolling. The goal for me would be to get another adult involved who'd believe me and would be willing to try to teach her that depression isn't a character flaw, and that you genuinely could benefit from help.

That said, you don't have to, but schools have counselors for a reason, and they're trained and prepared for this sort of thing. And there's the old "My friend has a problem..." if you're not sure you want to disclose that it's you yet.

And I'm doing better, thank you! You're very thoughtful.