Yes, Christmas cards to a married couple should be addressed to Mr. and Mrs. “And family” should never be used on an envelope. It is either assumed or is included as a note inside the card (e.g., “Please give my regards to your lovely family”).
I’d say that, in this case, your in-law did not intend to send the card to your husband as part of a social unit, but to him alone. Certainly husbands and wives are free to receive their own mail, even from family members. (Which means, by the way, that he received this card and not you.) While it may have been nice for you to be included in the greeting, there is no obligation that it be done.
If you want to politely indicate to your husband’s family how you and he would prefer Christmas cards to you to be addressed, then next year send cards to all of his family with your married names on the return address label (e.g., “Mr. and Mrs. John Anderson”) and then sign it with both names on the card. If you are the signer, it would be “John and Maggie Anderson” with your kids’ names on a second line in order of seniority (e.g., “Catherine, Monica, and Stephen” on the second line). If your husband signs, it is “Maggie and John Anderson” and then the kids’ names.
If this subtle demonstration doesn’t work, I recommend that you offer up the hurt and let it go. It’s not something worth making an issue over.
