The Photo Hunt
Put out the photo call and let your friends and family know you're counting on them to get this done. Give them enough time, but not too much time (there's nothing like a looming deadline to spur action!). It's likely the level of tech know-how varies in your circles, so let your aunt know she can snail mail some of her favorite photos and you'll have them safely returned. Then for your sister, tell her you accept texts, emails, Dropbox, Apple Photo Shared Albums, etc.