Does this really represent no brain activity after a stroke?
Let me first start by saying that as a stroke physician, I typically do not see patients with ruptured aneurysms - they are more commonly followed by Neurosurgeons - so please take this answer with "a grain of salt", so to speak.
In general, if your brother is truly following your instructions and answering questions, that is a good sign that you can expect further recovery over the next few months. I would not say he will "be ok", because I am not sure what would be "ok" for him. He may recover somewhat, but still need a feeding tube and assistance with his daily activities. For some, that would be "ok", as long as they are alive and able to interact with their family. For others, that would not be acceptable.
In general, a good way to predict his outcome is simply to graph out on a piece of paper his progress thus far, and continue that trend for another 3-4 months. That is likely where he will end up.
Finally, a CT would not show brain activity, rather, it would only show the brain itself. An EEG (electroencephalogram) might be a bit better for looking at brain activity and helping prognostication of his eventual outcome.
