Update on the kitties: the pills worked like magic. Within 3 hours of the first dose their tummies calmed down. No scary litter boxes in 3 days. I've been scooping the litter like crazy, and will be doing a deep clean (bleaching everything) right before their last doses. Had to get one of those pill guns to make it easier to give it to them.
Thanks to everyone for the kind words and ideas. Definitely helped ease my anxiety.