[Coffee.]

Honestly, I'd just bring it up to her. That's affecting you and your brother's quality of life. Be tactful. Heck, maybe just say "I've been hearing you both talking loudly in your room" or something, and she'll probably get the hint. That, or leave a note if you want to be a bit more clear about what you're hearing, as that doesn't put her on the spotlight but gets the same message across.