This is not your average discussion about what to vaccinate your horses with. That would be a discussion with your veterinarian, who knows you and what diseases are in your area.
However, to prepare you for that discussion, I will attempt to give you a bit about immunology, vaccination and disease history, and false advertising by vaccine companies.
You should NOT be anti-vaccines, but you should be aware that they are just one tool in your tool kit protecting your horses from disease.
In a nutshell: vaccinate for diseases that can kill your horses but for those that will only make a healthy horse mildly sick, use all the tools in your kit and vaccines.