Once in a lifetime

My husband and I have booked an 18 day Sydney-Honolulu Tahiatian cruise on the Carnival Legend. We've booked two rooms to accommodate ourselves and grandma who will watch our 3 children ages- 6,4,3 (it pays to be our babysitter).  Anyhow, the destinations (australia, fiji, new caladonia, tahiti/borabora) have always been on our bucket list and it seems we can bring the whole family on this cruise for (nearly a month) at the same cost airfare (to only 1 of the listed destinations).  So, this being the most EPIC family trip. I wanted to see if you have any advice/suggestions. We live internationally (Japan) and travel internationally once a month with the kids.... but, this will be our first time cruising. For cost (and balcony safety concerns)- we booked two side by side interior rooms in the mid section of the ship.  I'm a little concerned of claustrophobia---  Do you think its worth an extra 1k upgrade one of the rooms to an oceanview?  My other biggest concern:  I'm a bit of a health nut when it comes to feeding our family... At home we eat healthy local/organic food. I know that's unrealistic for a cruise, but due to the sheer length of this cruise, I want to ensure I can find some reasonably healthy choices, most especially for the kids. I read the kids options are: pizza, mac and cheese, hot dogs, chicken nuggets and unlimited soda. Reading that made me cringe. My kids are great healthy eaters. They are not picky and eat whatever mom cooks... a typical breakfast is scrambled eggs or oatmeal, lunch/dinner would be: soup, veggies (like spinach with beans) and a grilled fish with butter and lemon.  The kids have NEVER had soda, and I'd like to ensure it stays that way.  At home, they have reusable Nalgeen Sippy Cups that I refill throughout the day with purified water.  At dinner and breakfast they have whole milk.  I read the bottle waters are $5 each- are there any alternatives? Thanks