Hi Emily!
A first trip to Disney World is super exciting! I'm glad to see that you're planning ahead because January will be here before you know it!
Be sure to pick up a "1st Visit" button for each of you. If you're staying at a Disney Resort Hotel, you can pick them up when you check in. You can also get them at any Guest Relations location in any of the parks. They make great free souvenEARs!
Good idea to
rent a stroller for your boys. Their little legs will wear out quickly in the parks. I can't find the exact dimensions of the double strollers available for rent in the parks. I tried calling Guest Services but they didn't know the dimensions either. You can find a picture of the strollers for rent at Disney on AllEars.net. Its an unofficial website but they do an excellent job of providing pictures throughout the Disney Parks and Resorts.
You could bring a towel or blanket for the stroller. That way you don't have to worry about the size of the seat. Another idea is bringing two separate cushions. We bring the small kneeling cushions you use when gardening. They are small enough to put a couple in my backpack and they dry quickly if they get wet. We use them when waiting for parades and fireworks but they would work for strollers too.
Please feel free to keep the questions coming. We're thrilled to assist you!
Wishing you minnie magical memories :-) Allison V.