Hi, Tony. A better description of your doors would help. We don't even know if they are interior or exterior doors. They could be interior doors leading to a hallway, for instance. Some of the doors from that era were not much more than solid rails and stiles with pretty thin panels.
The most obvious solution is to replace the current doors with modern exterior doors that are either solid wood or with good insulation in the core. Solid wood doors will be expensive and will be a little louder that exterior doors with an insulating core.
Give us some more to go on and we may be of more help.