Now to the much more important dilemma -- your husband's browbeating and humiliating of your son. You mention that your son now seems "not really trying to improve". Do you think that you might stop trying to improve, or maybe even trying much at all, if you knew that your efforts would always be severely criticized -- if you knew that you would/could NEVER be a good enough ballplayer to satisfy your dad?
Unfortunately, your son's enjoyment of sport is being seriously affected by a dominating father with unrealistic, expectations. How can your son tell his father to back off and just let him enjoy playing basketball?
Your husband needs to realize the emotional harm he is doing to his son. See if you can get him to talk to a counselor with you about your concerns. Do not put your son in the middle of this. Maybe there is a male friend who could talk some sense into your husband in a non-threatening way. If he continues relentlessly pressuring and embarrassing your son in regards to his sports achievements, you risk causing deeper emotional harm to your son, harm that can and will damage his overall, healthy adolescent emotional development. Incidentally, your athletic daughter is not immune from similar treatment by your husband, especially if your son chooses to remove himself from sports.