Hi Christie,
Thank you so much for visiting the Disney Parks Moms Panel with your questions. I am happy to help you plan your magical Disney vacation!
How wonderful that you were able to enjoy a vacation to
Aulani, A Disney Resort & Spa. It is truly a tropical paradise! There is a
refillable mug program at Aulani. I spoke with a cast member there who confirmed for me that the mugs that you purchase at Aulani, A Disney Resort & Spa are for use for free refills only at that resort, and that refillable mugs purchased at Walt Disney World should only be used for free refills at Walt Disney World resort hotels.
As to
stroller rental at Walt Disney World, yes, the double strollers are side-by-side. The $27 cost for a multi-day rental is a per-day cost, so for four days, you would pay $108. Let the cast member know at your initial rental that you are doing a multi-day rental, and then save your receipt to show when you pick up your stroller on subsequent days to show that you have already paid.
I hope that this information is helpful for you, Christie! Please do let us know if you have any further questions.