I am a firm believer in honesty. You have all this information and need to process the best approach to sharing it. I think it is very important your husband is aware of how your sister feels. I can say if he is truly sweet and kind he would want to know and would not be offended at all. Is there a reason she is just now speaking up? Why hasn't she said something before?
I mean if you were hurting someone's feelings unintentionally wouldn't you want to know? Wouldn't you try to fix it?
I say, sit your husband down, when kids are in bed and say "you know, I was talking with my sister the other day, she mentioned a few things she felt really uncomfortable with what you said/did. I know you would never do that on purpose so I thought maybe I could talk to you about it"...
Keep the defense on low, explain what your sister said without adding anything other then the facts and ask your husband "you never meant her to feel that way did you?".
If he gets defensive just say "you are my family too and I love you, however I do not want to be in the middle of a feud here and you know how important my family is to me, so please, take some time to think about this as I would really appreciate you apologizing to my sister so the air is clear".
I was married to a very abrasive and non censored man. He thought it was best he was so up front, however he pissed off and offended so many people I was afraid to have him meet anyone. I was constantly embarassed and apologizing for him as he wouldn't do it! It was horrible. He was down right rude, all the time thinking he was a "honest man"...yeah right!
He would have blown a fuse if I tried to talk to him about how someone else felt due to his abrasive nature.
That kind of person you should be careful with. You should NEVER have to walk on eggshells with someone you are married to, you should never worry about being honest with them about something like this either.
I find it hard I guess him offending so many others in your family yet he is not like that with you? Is there a reason he may be acting like this? Does he like your family?
You owe it to them, you and your husband to sit down and talk to him. If he blows up, I highly recommend counselling. People should always want to know when they have crossed a line and try to repair it. If he handles the news the simply suggest he drop your sister an email, card, some flowers to apologize. All you can do is try.