Cleaner what? Shrimp? If that's what you mean they don't ever eat each other that I know of, but I'd think two would do nicely in a ten gallon. Each one likes to have its own lil space to set up shop and four would be a bit much I'd think in a 10 gallon.
Thankfully the 3rd one who's about a 3rd the size of the other cleaners just happens to have been crafty and found a home under a PVC pipe. I actually added a large CBS and everyone is happy together.