Hey there, Ashley!  Welcome to planDisney.
How exciting that you'll be sharing the magic of Walt Disney World Resort with your friends!  I hope your hearts will be full of magical memories, and that your 
My Disney Experience account is bursting with magical photos of your vacation together!
Yes!  You will be able to download your friends' photos, even if they arrive before you do.  It is helpful if you think of 
Disney PhotoPass service and 
Memory Maker as two different things.  Your friends are welcome to capture photos with Disney PhotoPass service as soon as they arrive.  If you are connected in 
Family & Friends and have 
set photo-sharing permission with each other, you should be able to view any photos your friends have captured in your account.  Your Memory Maker entitlement allows you to download all unexpired Disney PhotoPass photos in your account, including 
photos of up to 25 members of your Family & Friends List.  Currently, photos will 
expire 45 days after the date on which they were captured.  Your Memory Maker is activated once you download your first photo.  You then will have 
30 days in which to capture additional photos.  You are welcome to 
download any photos of your friends before you arrive, during your vacation, or even after you return home.  Keep in mind that Memory Maker allows you to download all photos in 
your account, but does not also extend to your friends' accounts.  However, once you have downloaded any photos of you and your friends, you are welcome to 
share them on social media, via email, or by printing through a third-party service.
I hope that helps!  Please let us know if you have any additional questions.  Have a wonderful vacation!
Anne Marie