So grateful your family can have this trip together. And yay for not leaving DD at home. I’ve had many little ones with me at WDW and characters are great with babies.
I do encourage considering enough stroller capacity for all your little ones. It has helped me immensely in crowds to have them (and their gear) contained/protected.
I’m loving following along with you on this!
Prepare for a dumb question, though: could you get an Ergo or something similar and prepare to carry DD1 while the boys take the stroller? I had something similar to this (not that brand, though) when my oldest was about the age your daughter will be and we carried her everywhere. There are also brands designed more for longer hikes. That way you could split up the kids (and have one parent take DD1 for an early nap, etc.) without having to rent multiple strollers.
In 2014, we went on our first family Disney trip to celebrate our (almost) 3 year old’s end of cancer treatment, followed by her wish trip to Disney the next year and we’ve been hooked ever since! I will be following along with your planning (as I’m currently building our 2019 Disney planning excel spreadsheet). Thanks for sharing 