I am in Kenya, where are you planning to go? Some areas are malaria free.
We are vaccinated against HepB/A/Typhoid/Men ACWY (over and above the regular UK vaccinations), however we live here. I would say Hep A/Typhoid are the most important and you would need to check Men ACWY.
I see you are keen on sailing, so yes Kilifi would make sense. Then you would be advisable to take malaria meds, malarone is the most effective. Also you would need to make sure your tetanus is up to date.......
I suppose you had better check with your dr as to whether you can all have the vaccinations with no side effects? Kilifi is rather lovely and the Indian Ocean is warmer than sailing down in SA I would imagine.