I have made more than 15 album quilts over the years for my kids, nieces & nephews.
I use this block :
http://www.quilterscache.com/A/AlbumTwistBlock.html
I cut the center square 6", iron a piece of freezer paper to the back to stabilize it for signing, otherwise it is very hard to sign without the ink bleeding.
Make sure you use a good quality fabric, tightly woven, like Kona for the center. Also use the Micron Pigma Pen for the signing. They work the best, and be sure to heat set it or it will fade.
There are 2 ways to get the signatures:
1 Have the blocks made and ready for signing at the event.
2 Mail the center square to the individuals for signature and complete the block after.
I have found it easiest to get the signatures at the event and mail to those who can't attend. This way you can keep control, otherwise you're chasing everyone.
If you do mail, send a stamped return envelope with clear instructions, you'd be surprised how people don't understand and what you get back.
Good luck, it's an awesome idea and they will love it.