i would definitely try to double the lights. that will put you around 38 watts/sqft.
normally i have read to try shooting for 40-50 watts/sqft + depending on the strain. right now your friend is running 19 watts per sqft which is pretty minimal.
he can expect what he gets.. too many variables to even give a good guess at what he will yield. guessing a yield this early on would be like taking 20 random babies and telling the parents exactly what they will grow up to be. there are too many variables involved to give an appropriate answer. at 19 watts/sqft i can tell you it will be a lot less than if he doubles the light.
My brother did about the exact same thing. He got 5 ounces off of four plants. It was very inefficient. Make the room smaller with some mylar or something if he can't upgrade the lights.