Wow! You know what you all need. The automatic scooping litter box. We have 3 cats, and they love it. We used to have one giant litter maid and a traditional box, but when I took the littermaid to clean it, we had a riot. Some inappropriate elimination, but I was NOT really mad at them. Every morning at 10 AM, they line up to poop. I didn't know this until after that day and promptly went out and bought another automatic box (because otherwise the first one could never be cleaned again).
With two automatic boxes, its great. They still que up, but its even funnier. I've walked in to find one cat in each box and then the other one waits until the box scoops and then she goes. And plus, its free entertainment for them. Sometimes, the box with start its scooping cycle, and they will all rush back to watch it.
So your cats are plotting against you. They've heard about the Littermaid and they want one or two (as is the case with my cat). A couple of weeks ago Petsmart had a $20 discount on both boxes online. If you printed out the online price, the store would honor it (which means your savings didn't get eaten up in shipping) And to top if off, my husband was on a two week exercise abroad when I got the second scooping box, and he said that it significantly cut the cat box smell.