I think the biggest problem with your tank, which you need to solve before anything else, is his lack of willingness to learn and improve. Perhaps because he's been tanking years in this 'friendly raiders' type of guild that he has assured himself he knows everything already and doesn't need your 'help' to get any better. Well he does. If you want to (be able to) improve you need to constantly question and compare why you do things a certain way and not the other. If you cannot answer someone's question about your spec/gear/playstyle in a logic, argumental way, this is the first step you need to take.
Because until you can do that, all other advise will simply fall on deaf ears.