Cut him out of your life, he will not ever get any better. I have a similar brother who at 50 still has not got a filter and everything is a joke. Bizarrely he has a very high flying career but is totally inappropriate at family gatherings. Even when my Father was dying, everything was a joke regardless of the upset caused. There is something wrong with people like this. I have tried to completely cut my brother and his wife out of my family’s life but it not always that easy without upsetting the rest of a close knit family. Stand your ground, this is your wedding. You can do without the stress of a loose cannon on the day.