Your husband is abusive (withdrawing/ignoring is abusive in this context) towards you, and now your son. And while he is doing this to your son, he's also ignoring you. You are being punished, op. You are being punished because of your son. You are not good enough to talk to, and now neither is your son.
You "have a word" with your son about his behavior, telling him to watch his tone (in order to placate your dh, and hope that your dh doesn't take his mood out on all of you) therefore asking him to walk on eggshells around his father., like you do.
Your dh meanwhile brings an innocent kid into this, speaking badly about you and his brother. Again, abusive.
It also says a lot that your dh cannot handle his almost adult son losing his temper without becoming heated himself, and taking it out on all of you.
I am not blaming you. I live with it (and more) too (although my dh doesn't ignore my kids yet), and I am making plans to leave, because no one deserves this.
Unfortunately many people don't see ignoring and withdrawing in this context as abuse, but it is.