If it's due to long-term deficiency of vitamin B12 like they obviously suspected, then there's not much you can do once there is permanenent nerve damange. :(
Definitely see about increasing his healthy fats - get rid of all margarines, phony foods, and replace them with real, organic butter, olive oil and coconut oil. I doubt it will bring back the nerves but it will certainly help with all the other things going on.
Is he doing any kind of cleansing? anything to become more alkaline? you always want to start there, especially when cancer is involved and it would help with the beta blockers too. It would probably be easiest to simply supplement his diet with a bit of Garden of life's Acid Defense with every meal.