We have gone with 12 before and the best thing we did was to all wear matching t-shirts each day. Besides being fun, it made it super easy to find each other. I saw my mother-in-law exiting the park through the tunnel under the railroad tracks when I was three blocks up Main Street.
Each of us had blue, turquoise and green shirts that stood out in a crowd. I had each kid pick their favorite Disney character and drew/traced them as a group, then added a title below the picture and had them printed on the shirts in black and white by a local tshirt/printing shop. The adults wore the same colors as the kids, but without the artwork. The kids loved their shirts (and still wear them) and we got lots of great comments. No copyright problems printing them because I drew the artwork.