If my private picture is in a private album, can anyone else see it?
The short answer is no, not unless you have invited guests to view or contribute to the picture or the album.
We take privacy seriously. If you've created a picture or album, only you decide whether it can be shared.
You can share a private picture or album with anyone you like. You can add a private picture to a private album shared with a larger group of people. Anyone viewing them sees who the owner is, but cannot share it.
The people you've shared it with can't open the share panel and don't get to see the email addresses or even the names of the other people the album is shared with. If you lose track of who a picture is shared with, you can check the share panel for that picture and you'll see not only the names of the people it's shared with directly, but also where it's shared as part of an album.