the diffuser here does not mean flash diffuser. it is a light diffuser. go to CP and ask for a 5 in one reflector and you will know it no time.
on the pics. WB is off, exposure is off, BG cluttered, focus is either soft or out. has all been mentioned. but how is it that no one mentions the poses on these pics?
case in point. look at michelle. #1, face perspective is big in relative comparison to the body.
#2, missing neckline. a pose like that needs to be done with care. right now, she has no neck and the indentation on the face caused by the shoulder pressing against the chin is really something that mars the picture even further. this picture honestly is bad in terms of angle of shooting. #3, exposure off is something, pose wise could be improved further. curves are there, but that is about as good as it is. #4, exposure is off, skin tones are off. but the expression is something that is left much to be improved on. the pout does not cut it.
something about portraits that needs to be understood is take your time to compose and look the overall picture first before you fire off your shutter. if you want to improve, take a leaf from some of the best here like bend1ck and hycool. it is not about PP. the shot matters more than the PP. if the shot is bad, PP can only do so much. it is not about shooting more, is is shooting more with a purpose and understanding the thought process before and when you are shooting.