Ushers duties/sister with autism

She could just be a greeter! That sounds easy and nice

Maybe she could help give out wedding favors if you’re having any? She could also help serve the cake or hold your bouquet during the ceremony?

You said FMIL wanted FSIL involved - does FSIL *want* to have a job? I think that's the place to begin. Then, if she says she would like to participate, ask her what she thinks she'd like to do from some options.

Ushers normally escort guests to their seats, so you could have her pass out programs/fans/whatever and still have your brothers as ushers.

View Quoted Comment Ok yeah! Just wondered if that would work, it sounds like it would!

My brother in law is autistic and he’s the same way. Tbh I even would’ve been nervous about him passing out programs because he can be pretty volatile when he’s in a bad mood, but hopefully she isn’t like that lol. He and my father in law walked my husband down the aisle during our ceremony. We felt like that was a nice way to include them without too much responsibility. He could definitely handle walking down the aisle lol, and it made him feel really honored and included.

Husband’s cousin is autistic. We don’t have her really do anything when we have events.
She’s pretty manageable when she’s by herself. Anything that involves her interacting with other people makes her freeze. So she’s not good in crowds.

Passing out programs seems to me like it would be a good job for her, because if she's not having a good day, either the ushers can do it, or people can pick up they're own programs. Wedding guests tend to arrive in an unsteady stream, so if you don't have programs, she can stand near the back of the aisle and say hello/tell people to wait for the ushers to come back while they're seating other people.