My brother-in-law is very ambiguous to me. What should I do?

According to your situation, you must resolutely refuse and be tough. Find a suitable opportunity to tell your sister the true face of this person, so that your sister doesn't have to pay so much for such an unscrupulous and bohemian person.

Tell my brother-in-law directly not to say such things to himself in the future. But it's best not to tell my sister. Because my brother-in-law didn't cheat in behavior, it was just language. I told my sister that if she didn't understand, she would think that being a sister-in-law was oversensitive. This is not conducive to the feelings of brother-in-law and sister, and it will also make sister doubt or dislike her in the future.