There should be a special park map for the event night, listing only the attractions that are open. On this, they have a small picture of a camera to indicate that you can take your family photo there. For
MVMCP, they had one in Adventureland (in the building across from the Treehouse), one in Fantasyland (by IASW), one in Liberty Square (across from the boat dock) and one in Tomorrowland (at the old Alien Encounter lobby).
We got in line at Tomorrowland, before the party started "officially", and were still about 10-15 groups down from the start, however later in the night we passed the Adventureland spot and it was empty (we got hot chocolate and cookies though).
Not sure why we got two photos if they normally send only one to an address? We did get two though, and we had two adults, two children, all living at the same address. They asked me how many adults when I filled out the address information, and I said 2.