My brother had a tramatic brain injury and lost his taste and smell. he still gets hints of a taste or smell but mostly everything stinks.

That can occur: Unfortunately, traumatic brain injury can result in difficulty smelling and the sensation of things smell worse than normal. I would consult an ENT doctor and or your neurologist for further questions.

Cribiform plate frac: He probably had a cribiform plate fracure. That causes a loss of the cranial nerve 2 (olfactory nerve) due to shearing. Loss of smell is very common. It most likely won't come back. Sorry.

Common consequence: The olfactory nerve courses through the brain and towards the nose through a plate with holes. When the head is subject to a force, there's a risk of shearing/ tearing of the nerve, resulting in those symptoms. As part of taste comes from sense of smell, taste is affected. It's hard to say the prognosis, but your brother should take more safety precautions- ie heat and smoke may mean fire closeby.