They do not share the same beach. The only hotel on Hapuna Beach is the Prince Beach.

We loved our stay at the Hilton Waikoloa! It does not have a beach right there. It has a lagoon beach with giant turtles that swim by you. There are lots of fish swimming around as well. The property is huge and with several very good restaurants. I was actually surprised at how good they were. We went with our teenage kids last year during Easter week. It was crowded for part of our stay close to Easter. We traveled around the island and snorkeled at some great beaches. We also took a snorkel cruise, but saw all of the same fish right in the lagoon at the hotel. We found Hapuna beach a great boogie boarding beach. I would not have been able to snorkel there. We had some great waves there though.
The Marriott is next door and a much smaller resort than the Hilton.
We also saw the Fairmont and it was nice, but also a lot smaller and quieter than the Hilton. It depends on what you like. We liked the hotel with all the action and amenities. Good luck!