sometimes if my girls aren't terribly dirty, but i think they're being lazy in the cleaning department, i just get them a little wet, which kind of prompts them to clean themselves better. i just get a washcloth and a bowl of water and go to where they're playing/sleeping. with young rats it usually does the trick; they kind of go, "what's all this water on me? i'll groom it off... and i'll groom it off of everyone else, too."
with older rats, i use a toothbrush and baby soap if necessary, usually only on trouble spots. i've had some old ladies absolutely refuse to clean the near half of their tails, which got pretty gross. a soft, wet toothbrush to scrub and a washcloth to wipe it off works.
lol If you ever figure out how to get them to stop peeing, let the rest of us know?
If just just keep their cage spot cleaned, the peeing on each other will diminish. If the cage is *too* clean, it can cause them to mark more to make things smell like them.
If they sleep in an igloo and smell bad, change the bedding the in igloo more often. I have 7 rats, and I change litter boxes and igloos twice a week. If they sleep in a hammock mostly, try washing them more often. Hammocks really tend to 'spread the smell around' too.
Also, providing them with a heavy, shallow dish of water once in a while may encourage them to clean. A lot of rats will generally use the clean watter to wash themselves a bit.