Ok lets see if i can say it right.. I have a chihuahua mix, and 2 boston terriers. One boston is a boy, the other is a girl, and the chi mix is a boy.. All our dogs are Kennel trained. So at night they sleep in them. In the morning when we let the dogs outside to go pee. If we dont go outside and watch, the Chihuahua pees on the little girl boston. EVERYTIME!!! its disgusting. Anybody know whats going on?

It is really disgusting...
I think your dog Chihuahua need a proper behavioral training...
Oh poor little girl boston...

If the chi is fearful, he could be trying to "hide" his scent on the (more dominant?) boston.

You could always let the chi outside first and give him enough time to pee before letting the others out. Over time he will get used to peeing where he's supposed to and forget he likes to pee on your girl. Hopefully.

It sounds like a territorial marking thing. The best product I have seen to help with this is the Happy Jack Dog Diaper. You can pick them up here: Happy Jack Best Dog Diapers - belly wraps with the non-slip strap