Just wanted to let you all know that I think we've got it under control. The pumpkin didn't work - not one of the 4 cats would go near it. I tried to force feed a couple of them and my white kitchen floor as well as the blinds over the windows was spattered with orange pumpkin goop. I ended up sprinkling Metamucil onto their dry food - which by the way, is hairball food that the vet suggested. One of the cats will eat canned food and she's getting Metamucil in it every night. I'm noticing more poop in the litter boxes each day so it's working. Thank all of you so much for helping me out with this. Siva, Wooz, Sweets, Chex and I all appreciate it a great deal.
Ms. Z, the site you mentioned was most informative. I learned a lot and am now better able to spot a problem before it gets too far along. Thanks!