My brother and I took on the coordination of the big family vacation. My brother found the enormous beach house and I invited everyone and ordered a catered dinner, as well as coordinating how all the regular meals happened for the week
I also convinced my brother to steal their stashed away photos and slides and digitize them. I think he digitized them all, but he also created a fun family slide show to present during the vacation. He pulled his computer out with each of the elder generation and got them to tell him at least the names, if not the stories, and recorded all of that.
One of my nieces created a scrapbook that included some of the more recent pictures and she got everyone to say something nice about them that she recorded in the book.
Depending on the vacation they have planned, could you add something spectacular on to it for just the two of them, like a balloon ride or a helicopter ride?
Do they currently have family tree art of any kind?