Do you by chance happen to have a low-priced UV or haze filter on the front of your lens? Because all of these have a very hazy, "flat" look to them...and it looks almost like it happened at the time of capture, and not in post. WHatever the lens is it produces unpleasant, nervous bokeh on the out of focus foliage and woodland type of background scene you have in this session. There's just an unpleasant nature to the lens used...the pics are not fuzzy enough to be considered soft-focus or arty, and not sharp and clear enough to be viewed as modern, digitial images...they fall sort of in-between.
I think the one of him opening his shirt to reveal the Murica T-shirt would look better cropped to a square, eliminating the big tree behind on the left of the frame. On the one with him and his phone, I'd try and elevate the exposure on his face a bit, and boost the contrast on the shot, maybe go with a crazy "effect" processing look, like a cartoon-like color, or a very high-contrast, four-tone B&W "litho film" type look. Not sure about the squatting down shot, but the last one is okay.
My honest feeling is the best way to make your brother's senior photos better is to re-shoot the session with a clean lens, and a good lens that will produce nice, contrasty images. I am not confident that editing is what will improve these; a re-shoot would be a great way to get more material to work with!