With everyone "grown", the family counseling thing sounds a bit odd to me; it's not like there's a child having a problem? You all are two different couples and it sounds like your mother-in-law hasn't thought things through. Any "good" counseling is going to strengthen the relationship between husband and wife in this situation, not mother and son? She'll "lose" her son worse! She's the one who doesn't belong in the "family"?

It has to be hard with your husband working for the family business and, I assume, your father-in-law taking orders from his wife :-) The three of them have opportunity and need to be together so almost have to talk about family and interactions, etc.

Were I you I'd decide what I personally wanted for your and your husband's marriage and discuss it with him, asking him not to discuss it with his parents. If you want your husband to leave the family business, I'd tell him that and brainstorm ways to do it. If your mother-in-law finds out stuff from your husband talking about the two of your's relationship/marriage conversations, I'd maybe get some marriage counselling so he learns to separate his marriage from his family business interests and refuse to share things about you in the business setting?