Its been a few years since I was last on Maui, but there have been more than a few threads on the various Maui properties:

Grand Wailea or Marriott/Renaissance Maui
Marriott Maui Ocean Club on points - How likely?
Maui Renaissance Wailea update
Best Hawaii Property
Is there 3 or 4 Marriott properties on Maui?

These are all fairly new. If you do a search on the Marriott forum with the term "Maui" you will find these and many more. Hopefully, one of them will have some good info for you.

As for how easy is it to get award reservations at the various properties, well that depends on a couple of items. One is the MVCI property will be almost impossible to get using points. It never hurts to try, but the chances are remote at best. I think the Ren is being decommissioned, leaving only the Marriott Wailea. I would suspect that if you plan well enough in advance, you shouldn't have a problem getting an award stay there.