Hi Henrique!
Welcome back to the Disney Parks Moms Panel. It sounds like you are planning a grand adventure! Walt Disney World Resort is the best place to vacation when multiple generations are tagging along, as there is something for everyone to enjoy, from grandpa to babe. I also think that there is something magical about experiencing the 'World through the eyes of a little one. The Resort is magical at all times but is sprinkled with extra pixie dust when a baby is involved.
You mentioned that you own at Disney's Polynesian Villas & Bungalows. That's fantastic because it's one of the Resorts I suggest! The Deluxe Studios are spacious and come with a split bathroom, which is super helpful when you have a baby. One parent can do bathtime while the other can simultaneously get themselves ready. I also love the convenience of it being a Monorail Resort. You are a quick trip away from Magic Kingdom Park, and within walking distance of the Transportation & Ticket Center, from which you can jump on the Monorail to EPCOT. Also, you can catch the ferry to Magic Kingdom Park, which is our favorite form of transportation with the littles. There is no need to breakdown your stroller, and kiddos love the boat ride and view!
In general, when you travel with both babies and grandparents, convenience is critical. That's why I love Bay Lake Towers at Disney's Contemporary Resort and Disney's BoardWalk Villas (which are both usually available to book at seven months). The Towers are a quick walk to Magic Kingdom Park (about five minutes!), which is convenient for all. No need to jump on and off of transportation, and you are close enough to return to your room for nap-time. The same holds for Disney's BoardWalk Villas. You are approximately a 15-minute walk from the Planet of Batuu, and 10 minutes in the other direction puts you at EPCOT's International Gateway and the fantastic Disney Skyliner! Disney Skyliner connects four Resort Hotels and two Theme Parks, and the gondolas are big enough to roll the stroller right on. All of which equals less stress for papa!
Henrique, when you visit, make sure to take advantage of the Baby Care Centers. They are a cool, relaxing place to take care of all of your baby's needs, and I'm sure grandma and grandpa will appreciate the air-conditioning and comfortable chairs! If you have any other questions, please don't hesitate to come back. ChEARs to a magical vacation!
Rayna