Hiya
My personal opinion is let him be! If that is the way he feels most comfortable with your family and friends and he's not downright rude to them, then let him be himself. Just stop mentioning it and let him come round on his own. Just say to friends and family that he tends to be a little quiet in company and leave it at that. In time, if things are going to change, then they will otherwise just accept that that is the way he is.
xxxxx