I wouldn't say anything at all.
If none of the other family members know anything about your conflicts, then now is certainly not the time to spring it on them or cause any drama.
Even if you are somehow seated near your brother in law and his wife, you don't have to gush over them, but you can certainly be cordial for a day in order to be the bigger person.
Set your feelings aside for the sake of the couple getting married and for the rest of the family.
The wedding is a month away. No doubt the bride and groom are in a flurry trying to pull everything together and make sure everything comes off without a hitch as it is. This is no time for bringing up discord with other family members.
A) You don't know even IF you will be seated by them.
B) People tend to move around and mingle at receptions after the initial toasts, etc anyway.
This day isn't about you or your brother in law or any conflicts you have had. When you think of it that way, it might be easier to set things aside for a short time and just enjoy the event.
That is my opinion and advice.
Best wishes.