OP, maybe I missed it but did you ever clear up whether or not it was your husband who told you your MIL was upset about the address labels, or she told you herself?
Like PPs I have to say that your husband seems to not only have no interest in mending fences between you and his family, he's setting it up to make it worse. If I was trying to make it right with my wife, I'd be on my best behavior. If this is his best behavior, I'd say there isn't much future in this. I'm sorry. I feel for your children who are likely to feel the tension between you, your DH and his family. Kids aren't stupid to not notice their family isn't speaking to their mother - especially over three days, on Christmas.
Why did your DH need to leave to spend time with his family at 5pm on Christmas if you were already spending three out of four days with them? Aren't you guys his family? I credit you in a way for sticking to this, but I'm confused as to why you'd want to endure such treatment, and have your kids endure such treatment, another day.
Bottom line is the problem is not your inlaws. It's your husband, and yes he was rude.