The wedding has not happened and his family is already talking crap about your family. Your fiance is already starting to make excuses for their behavior. This was arranged so its not like you’re super “in love” with him.
Can you please explain why you even want to go through this marriage right now? Do you honestly believe their behavior will get better AFTER the wedding? Right now, this is their “best” behavior.
Do not for a single minute think that the in-laws will change after the wedding. And it looks like your fiance is already making it clear that he will stand by his family. You really need to think about whether or not you want to spend the rest of your life dealing with this behavior.