An Ex-Family Reunion
Of course, when a man becomes your ex, his relatives become your former in-laws. Depending on the circumstances, they may also have formerly liked you. Do you really have to extend the guest list to these people who constantly badmouth you, who will no doubt make you feel uncomfortable, and who will only serve to dredge up images of days gone by that you would rather forget?
If this were your wedding, you could completely discard these folks and surround yourself with people who would only heap praise and compliments on you for the entire day. Of course, this isn't your day, no matter how much money and energy you've put into it. Your former relations are your daughter's blood relatives, and as long as she's not actively doing battle with them, you have to respect that bond. You can't exclude your former mother-in-law, because as far as your daughter is concerned, she's Grandma. What's happened between the two of you must be put aside for one day.
You'll be incredibly busy on the day of the wedding, looking out for your daughter, making sure that everything's going according to plan, and you won't have time to worry about what your former brother-in-law might be saying about you at any given moment. Unfortunately, some folks go out of their way to start trouble by initiating face-to-face confrontations. A wedding is one of the least appropriate places to revisit old arguments. Your best bet is to simply ignore anyone who tries to pull you into a fight. If the behavior is really out of bounds (shouting, cursing, etc.), you have every right to ask the troublemaker to leave. Your daughter and her groom (and his entire family) shouldn't have to bear witness to such ugliness on their big day. You also can tactfully suggest seating arrangements to your daughter. Your daughter probably knows you better than anyone else, and will in turn do her best to protect you (and her wedding) from troublesome encounters.