There is a 45 day window before pictures expire, so as long as you both get your photos taken within that window you should be good.
There is also a 30-day limit once the first photo is downloaded from memory maker.
Your friend will be the “Leader” account for the memory maker.
Your friend needs to add you to their friend and family list.
In your MDE account, find your friend (the leader account) and click on edit permissions.
Make sure Share Photopass photos is checked.
That should do it.
There is a document and many posts on the forums that talk about how to share memory maker. Look at that to get all the nitty-gritty details.
Also @OBNurseNH mentioned how to make sure your photos are seen in the “Leader” account in this post…