I am always confused when I read a bad post about Ohana. We go there every trip at least 2-3 times and LOVE IT! It's tied with one or two others as our favorite, and for us its an absolute must do.
Service can be fast, so I recommend you tell your cousin that you that you will let them know when you are ready for the next course. This really helps.
As for people who say they never saw their servers come back, well I can't imagine not just grabbing any sever in sight to help. You really have more than one server. There are two or three servers that will be bringing the various different foods. We have always found the service to be very good and dispite what others have said, the food to be very good. In fact their salad dressing, chicken wings, grilled turkey, and dessert cannot be beat!
I know some people do not like the Ohana singer, some are better than others. But the entertainment is geared for the kiddies and as you will see, the children ALWAYS have a great time.
Remember what they say about opinions.
There is a reason this is one of the most popular places at WDW, always booked and difficult to get an ADR. Try it for yourself and let us all know what you think.

I think you will be reporting very good things.