The hotel should have vans available for families, groups, or people with lots of luggage, etc... I am sure you could arrange to be picked up at BKK in a larger vehicle than their BMW 5 series if you need more space.

I don't know about scheduled flights to Hua hin, but I remember hearing that they at least used to have some.

I know that the Intercontinental Hua Hin has its own Cessna Caravan, and there probably are other options for private planes.