So, your non JW daughter is inviting JW relatives and ex JW relatives and she is supposed to be a hall monitor? Or you are?
I would not own that at all. Figuring the numbers for the reception, only count half of the acceptances of the JWs (no sense in paying for the ones who walk out before eating) and realize that you are not responsible and should not be HELD responsible for this-however, if you will be DFd for this infraction(!) then you need to consider whether you will go to your own daughters wedding. Seriously, This is so whacked. Do you really want to even open the BOX to this game?
Dear Abby would say that you don't have to interphere at all. If they want to be idiots, that's on them. Hope they leave the present!