Hello Lily,
I recently contacted a immigration law office. She said the same thing, a lawyer will not make any difference with the current delay. And yes, changing case being a citizen will be back to square one and new expense for new derivative.
It's pretty much a waiting game like with your brother. Maybe there's a way for him like a child protection? I already emailed NVC. They just said the same. Just to wait.
Good luck to you as well and thanks for your help!