Memory maker (Or the photo dowload entitlement that comes with APs) entitles the holder to download any pictures that are active in their account at the time. Linking other people through Friends & Family (and making sure they are set to share pictures) lets them show up in your (Memory Maker/AP holder) photo stream. As such, they are active pictures in YOUR account, and YOU can edit/download them. So while your linked Friends & Family won't need to purchase Memory Maker themselves, technically they aren't the ones using it, YOU the AP/Memory Maker holder are.