How can I stop an older cat from attacking? I know he is scared and disoriented in a new home and new people?

that seems to be a stress issue for your cat and that is why is reacting like that. I would suggest you to spray and plug-in Feliway www.feliway.com/us it contains pheromones, when this is present in the ambience, it makes the cat feel safe and comfortable. Its completely natural and helps cat reduce stress such as moving into a new place, travel, or be with new pets. Good luck :)