If you are reserved in the Hawaii Building - you must have reserved concierge rooms. Did you reserve lagoon view or garden view - that will determine only what side of the building you are on. The lagoon view rooms are significantly more expensive, and they rarely will upgrade you from garden to lagoon.
That said, you should have no trouble at all requesting a ground floor room for your parents and brother's family, since your parents are elderly and may have mobility issues. The rooms on the first floor have a patio, while the rooms on the 3rd floor have a full balcony. The rooms on the second floor only have a slider - not a stand-on balcony. Sounds like you and your sister will want to request 3rd floor, although you may like being on the first floor with the rest of your family.
The lounge for the Hawaii building is on the 2nd floor - that is where all the food offerings are served - It has a huge 2 story window that overlooks the lagoon, and Cinderella Castle!! Great for viewing the fireworks - they even pipe in the music!
Hawaii is right near both the themed pool and the quiet pool, and just a short stroll to the boat dock. It is a wonderful location.