Hi,
I'm thinking of getting married on a private estate too! I've found one Hawaii Kai, Hawaii vacation rental by owner: 5 bedroom Oceanfront Estate rental that sleeps 15. Ocean Beachfront Banyan Tree Beach House it looks amazing on the website and they allow for weddings but charge a fee. I'm going to Hawaii on 20th May to check out venues, I have this one, Ko Olina and Turtle bay resort (yes Pura is very slow at replying unfortunately... her assistant is better), I have a meeting set with them.