Hiya Kate!
Thank you so much for stopping by! You've asked a fantastic question! Stroller rentals are a very important part of a vacation with young ones, and it can definitely make a difference to help make those little legs go a little bit farther at the end of a long day.
The
strollers available for rent at all Walt Disney World Resort theme parks will have a maximum weight capacity of 100 pounds total. I say this because your girls' combined weight is already above that limit. Going over the weight limit isn't recommended and will definitely make the stroller more difficult to maneuver. The strollers are really optimally designed for children under 45" tall, so it might be a bit uncomfortable for your older daughter, especially when she has to share leg room with her sister.
Off-site rental options will also have a similar combined weight limit on a double stroller of 100 pounds. The City Mini GT double is going to have a bit more space--allowing up to 49" in height, but the combined weight limit is still listed at 100 lbs. The single version of the same stroller (City Mini GT) would have a 65 pound weight limit and 49" height limit. This could possibly be the way to go with your girls. I know once ours were a little older they would happily take turns 'swapping out' with their baby sister in the other side of the double stroller. You could easily use a single stroller in this capacity as well!
If you're looking to rent from a Disney Featured Provider, you'll need to make sure you rent at least a month out. I've personally rented from Orlando Stroller Rentals, and have been super pleased each and every time with the service.
Have a magical vacation!
Amanda