I would say you were right and wrong. You were right to tell her that it's her fault for getting so little sleep that she has to scold her 7mo old baby and wake your brother up. That lets her realize that maybe she should be doing things differently. The only way I'd say you might be wrong is in your delivery. In an ideal world, you would have been firm and assertive about your thoughts without adding ridicule to your words. But 6am with a crying baby and a frustrated mother is hardly a perfect world. So eh, I'm no expert but I agree with fatbooty in that you should all have a nice calm talk about what should be happening when everyone's awake.