Do I tell my future SIL that I don't want her son at the ceremony?

My fiancé's SIL's son is severely autistic, non-verbal, and prone to making a lot of noise and having outbursts. I feel bad, but I don't want him to disrupt everything by screaming or running around (which I have witnessed him do). I feel that the wedding ceremony is sacred and I don't want people there who can't treat it with reverence. I would just explain it to my SIL, but she is very easily offended and I don't want to cause a big problem. What should I do? via /r/wedding http://ift.tt/2sUQ9CR