His Sister as a Bridesmaid?

wolverine0610

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bablingbrooke

Ask the cousin if you want the cousin up there with you.  Then gauge FSIL's reaction.  If she's upset, ask her.  If she's not, stay the course.  Most mature adults won't get upset about this, and fewer will ask why they're not in the WP.  But if she makes a fuss, you can still ask her.  Or your FI can have her on his side--gender isn't an excluding factor.

Don't make your decision based on how many guys he has.  No one really pays attention to the symmetry of the WP, and most people who make decisions on that basis regret it.  Seriously--eliminate it as a source of consideration.  Pick your side based on who you want standing next to you.  Begin and end with that consideration.  

bablingbrooke

It's not FMIL's decision, so if she reacts poorly, just say, "Sorry you feel that way, but I've made my decision."  And then your FI needs to come to your defense, or change the subject, etc.

Don't come up with jobs for people who aren't in the WP.  Coming up with a job for someone so they feel "included" expires around age 9.  Adults understand that not everyone can have a part.  And to be perfectly honest, most people would rather wear what they want and attend as a guest.  Wanting to be a guest and supporting the marriage are not mutually exclusive.  I can tell you that for most of the people in my life, I'd rather be a guest than in the WP.  

You wouldn't have to trade sides, but your FI should only ask your brother if he wants him on his side, not because of any pressure from you or your family.  That would be hypocritical of you.  I'm sure it's not the case, just throwing that out there.

bablingbrooke

It's a difference of one person.  If it's causing you this much grief to not ask her, just ask her.  It's one person; it won't change a lot.

My sister and I were not close, I still asked her to be MOH, she was uninterested and then actively tried to sabotage several pre-wedding parties, had meltdowns during them, etc. (we later found out she was bipolar but she wasn't diagnosed/treated until a few months after the wedding).  I would still ask my sister again because she's my only sister and will always be my sister, even if I fall out of touch with all my friends who were in my wedding.  I'm glad she was a part of things.  Yes, I wanted to strangle her sometimes, but I'm honestly very glad that 1) I never lost it, though it wasn't easy, and 2) that I reached out to her.  Our relationship is better now that she's got some treatment and we understand each other better, and I don't know if that would be the case if I hadn't done so.  Don't know if this is applicable to you, just sharing what I went through.  

ETA: This isn't to say that the wedding will bring you closer; frequently the opposite happens.  I'm just saying to take the long view.  Will you regret in 5 years leaving your FSIL as the odd sibling out, or will you be glad you erred on the side of inclusion?  I know where I land on that, you need to figure out where you land.