I'm happy with it whatever I call them. As far as I'm concerned, creating jobs for people who want them is a good thing. I don't see why people are so down on cleaning. I have done cleaning, and I've done other work, and IMO cleaning is better than factory work, cashier work, telesales, call centre and working at the hand car wash. It's flexible, it's usually warm, you can watch TV/listen to music.
However, I think they can only be called staff/employees if you employ them full time (i.e. you are their employer). If they're just coming in for a few hours a week and have several other clients, they're self-employed and basically run a cleaning business.