Hello Pamela,
Welcome to the Disney Parks Moms Panel! I'm a big fan of
Memory Maker and purchase one each time my family visits the Walt Disney World Resort. It's a wonderful way to capture your entire family in all of your vacation photos! All photos taken by
Disney PhotoPass photographers are included, as well as Attraction Photos and Videos, Magic Shots, and Dining Photos. All photos that are scanned to your
MagicBand, and the photos of those in your party who have enabled photo sharing with you, will be available for you to download.
As long as your Memory Maker is linked to your
My Disney Experience account and you have enabled photo sharing with your sister-in-law and the other members in her family within the "Family & Friends" list, then you will all be able to use one Memory Maker. Enabling photo sharing with everyone in your party will allow any photos taken to be shared on your Memory Maker even if you arrive at different times or split up and do separate activities during your trip.
I hope this information helps. Pleas visit us again if you have any additional vacation planning questions!
Magical Wishes,
Susan