I'll give it a shot.
#1 - I'd bump the exposure some. Her face is twice as dark as her hands - I'm assuming she's wearing a lot of makeup, may not have been your fault, but it's distracting. WB is ok.
EXIF data tells me you shot in Av mode, at ISO 400 with a 1/1000 sec shutter speed. 1/1000 is waaaaay faster than you need, especially at 85mm focal length (at f/2 I'm assuming it's the 85mm prime), to shoot a static portrait. You could have easily reduced the ISO & shutter speed. I say this mostly because the camera is an XTi, and I shot an XTi for longer than I should have, and its noise performance... leaves something to be desired. I don't see a lot of noise in your shot, but I wouldn't run the ISO up over 200 on that body in situations you don't need to. I also say this because I think you should learn to pay attention to all 3 elements of the exposure - aperture, shutter speed, ISO - and know what your settings are before you take the shot. Teach yourself manual mode, and do it now from the start before you get further into this. It will force you to do just that, and it'll force you to pay attention to and keep up with changing light situations. Learn to use the most ideal settings for each shot you take to produce the exposure you're looking for. Personally, ISO is the very last thing I will compromise on due to the noise factor.
#2 - again a bit underexposed, but also too cool. Look at the whites of his eyes - they are blue-ish.
#3 - Better exposure-wise, but lacks contrast. WB too cool. It's tilted, the treeline and "booth" lean to the left. Really cute idea though.
Are you post processing these at all? Are you shooting RAW or JPEG?
Well I've gone off on a tangent here, beyond critiquing the photos themselves. All 3 have potential and you're off to a good start. The XTi is a great little camera to learn on. Keep shooting and posting!!