Apparently I am the only person here that thinks it is not your FI's job to control his mother. The two of you are getting married, the two of you are planning a life together, the two of you have to form a united front against his mother and work together. If you dictate to him everything to tell her, you are acting like the manipulative and controlling bitch she is going to call you her friends and family. If you have an issue with your FMIL, you have to discuss it with FI and the two of you need to agree that his (or your) mother is out of line and the two of you together need to prepare an argument against her and sit down together with her and work it out in an adult manner. By sending FI to do the dirty work you are setting yourself up to angry with him once you realize that he is not putting the same effort into getting your way as he it.