How about a scrapbook type idea. Give each adult a disposable camera or if they bring their own camera a roll of film. Maybe even give each person a couple of themes. Such as the 4 of you, animals, plants, signs, characters, sunrise/set, CMs, transportation, rides....
Then after the trip if you still get together quite a bit you could do the following. Develop the film and get double prints. Buy mini sized scrapbooks, one "tool" each or loan them each a tool, them give them some identical items. For example "Joe" would get 4 identical blue papers, 4 red papers, 4 Mickey stickers, 1 marker.... Match the items to the person and theme. If Joe has great handwriting he gets the marker. If Fred has bad handwriting give him letter stickers or pre-made messages. Each person can use their items to make pages for each of the 4 books.
Or if you're a scrapper you can make up each of the 4 mini books for them.
Another idea is
letterboxing Read the FAQs and all the info for an explanation. There are a set of 3 that are in CBR, WL, and Celebration. Then there are 4 separate ones to find at WDW.