Can you buy park tickets at the hotel to Get the early admission ?

You can buy tickets at the hotel, staying at Cabana Bay gives you early access

You don't have to buy ticket in the hotel to get early admission. You can buy your ticket online anywhere cheaper and use your room key in the park to enter 1 hour early.

Yes

Your room key gives you early access to the parks. Pick Harry potter if you go early or something with crazy lines. Still took us 30 minutes in line when we got early for Potter's castle which was the best ride.

Yes you can, but it's most likely more cost effective to get them prior by shopping around.

Just need your room key for early access from any universal hotel. Its only good for Harry Potter worlds and Volcano Bay.

Just staying at Cabana Bay gets you in early to the parks if you have a park ticket. And yes you can buy a ticket at the hotel.

If you purchase the package deal with the hotel you will get the early access, I'm not sure about purchasing the tickets at the hotel. The early access is ONLY good for Island's of Adventure.