Wedding Party

You can't force relationships to be close with a wedding or a wedding party. Put your brother on your side. Don't bother including FSIL. All of your family will be at the wedding and are already honored guests. If you want to give them more attention, you can list them in a ceremony program.

To answer, your question you don't. Neither of you should be deciding for the other who is on each others side. It is up to the groom who the groomsmen are and it is up to the bride who the bridesmaids are. If it is important to you that your brother and your BIL are in the bridal party then have them on your side as bridesman. Your fiance told you he's not comfortable with them as groomsmen so you need to respect his feelings. You can't expect him to respect your feelings about your SIL while you are disrespecting his feelings about your brother and BIL. Have them on your side or respect your fiance's feelings and just have them as guests. My brother was my bridesman so it's definitely not unheard of having a guy on the bride's side.

You are absolutely not wrong to not have your FSIL in your wedding party. It seems very obvious she intentionally excluded you from her wedding, and that she is not interested in forging a relationship with you. However, it isn't up to you who your fiance has in his wedding party. If it's important for you to include your brother and BIL, simply have them stand on your side. Mixed gender wedding parties are super common these days, as are uneven sides. Just make your brother and BIL bridesmen, and let your FH choose his party.

I'm going to disagree with that last part. It sounds like Fiance only requested the SIL as a swap for adding the brother and BIL.

OP, I know you have your suspicions, and personally I think it was rude to be seated away from your partner, but I would let all that fall off your shoulders. It's the parents that cultivate family favoritism and both SIL and your FS have been treated unfairly to the point of rivalry. Just move forward passed the toxicity. Whomever you and your FS choose should be your own decisions. Don't fill these honored roles with arbitrary guidelines like future in-laws, siblings, and single- gender sides.

With you having 2-3 men in your wedding party, I don't think you have to worry at all about "incorporating them without making it feel uncomfortable to be on the 'girl' side"; as nearly half of them will be male. I had one bridesman on my side, and the rest were females, and there was no awkwardness at all. Our sides were also uneven, and no one thought anything of it. Our pictures turned out great (both the posed photos and the candid ones of them at the alter) - it didn't look strange or lopsided. There is also always the option of having all wedding party walk down the aisle, then having all of them (or all of them except the maid or man of honor, and best man) sit in the front row.

Google photos of mixed gender wedding parties. It all looks really fine, actually. I don't think your FI should feel obligated to have your important people stand with him.

Uneven wedding parties are fine, as friends and family don't come in matched sets. The size is significant with what you have planned, but you could have everyone walk down the aisle and take a seat in the front row, leaving maybe one person for each of you to stand at the altar for the service.

As your FI's brother's wife, your SIL had no obligation to include you in the wedding party, and that's not really a rule. She was rude to ask you then leave you hanging on the wedding day, but it may have just been an oversight during the excitement of the day.

While I also think all things equal it's a generous thing to include FSIL and FBIL in the wedding party, not everyone has that mindset. Maybe she thought it would cramp her style or mean having to invite you to her bachelorette etc. She could have had you stand up in the wedding ceremony regardless, of course. I can understand FI's point that it looks petty and intentional to exclude one future sibling in law. Did she or her H have other BIL or SILs in their bridal party? If so, and they were not included is it also possible she felt she needed to be consistent?

As for the getting ready drama, I would have asked her what time she wanted me there the night before or when she asked you, not expected a text on the busy morning of her wedding. And she was literally right next door, so I really don't understand why didn't you just poke your head in and ask once the guys were coming to your suite if not before.

On another note, swapping seats wasn't appropriate on your part. They have the right to make their own seating arrangements. I don't care for the practice at all, but some couples choose to put bridal party together. There's nothing inappropriate about it, though.

The bigger picture is the relationship itself. For the sake of family harmony, I would continue to be cordial. Nothing you've said rises to the level of a confrontation at this time. If things become more blatant then maybe it would be time to have an open discussion, but I don't see anything good coming from it now.

As for the bridal party, I'd probably suck it up and include her if having the brothers is important to you. You could have the guys on your own side as others suggest, but having FI ask might be a nice way to recognize their new family relationship.

You don't need to include your sister in law if you don't want to. In reading your post, it didn't seem to me like she was intentionally leaving you out. It sounded more like it slipped her mind because she had so much going on. You also don't mention bringing up your concerns with her directly, so she may have thought you were okay with everything. I agree with others that it seems the parents have fostered a rivalry. It may be worth having a candid conversation with your sister in law about your feelings.

As for the mixed gender parties, they're really common now. I have men in my group and my fiance has women in his. We let them choose whether to attend the bachelor or bachelorette (or both) and which group to get ready with on the day of. It's working out really well.

"It seems like I’m going to have to suck it up and ask her, which is honestly pretty upsetting to me." Why would you do this?! She isn't close to you, and has actually gone out of her way to be exclusionary toward you. Why would you invite that negativity into your wedding party, (and then subsequently into your bachelorette party, shower, and on your big day)?! Ask your brother, BIL and male friend to stand on your side. They can decline if they feel "uncomfortable" for some reason (which tbh, is absolutely childish and ridiculous because their role would be to support you and your relationship- not segregate themselves into "boys and girls" like school children). At that point, they cannot be angry with you or hurt for not being included because you attempted to include them - it's not your problem if they choose to decline. Your side should be your nearest and dearest, and your FH's side should be his nearest and dearest. It certainly should not include either of you being coerced into including people out of guilt. And while we're on the subject, I would have a HUGE problem with my fiance if he handed out an ultimatum that meant including someone who so blatantly disrespected you and your relationship, and who he knows would create a negative experience for you surrounding your own wedding! On the other side of that, it is also not ok for you to try to force your family members into his wedding party. I think by presenting you with that horrible ultimatum, he is hoping you will understand his feelings and you will rescind your request. Don't force eachother to include people in your wedding parties - it is only going to cause resentment and possibly ruin the wedding experience for both of you. You only get one shot at this - don't ruin it for yourselves or each other!

Family dynamics can be tricky, some people just don't mesh well for whatever reason. Personally I think a wedding party should include your nearest and dearest I don't think anyone should be included out of obligation. Since it sounds like you and your FSIL don't have a great relationship I don't find it odd that she didn't ask you to be in her bp or extend an invite to thebachelorette. As far as the morning of the wedding she probably knew the guys were going to be using your room so extended the invite but wedding mornings can be stressful she may have forgotten. I would have just texted her or knocked on the door. You are under no obligation to ask her to be in your bp but it may improve your relationship with her moving forward (or maybe not who know) but your fiancé also does not need to include your family members on his side. If your brother doesn't want to stand on your side you can always ask them to be ushers or do a reading during the ceremony. I think some of the best life advice I ever received was don't make choices based on what others have or haven't done for /toyou make your decisions based on what feels right to you and best for you. Congrats on the wedding and happy planning!

I totally don't think you should include anyone out of obligation, that's the source of a lot of the wedding party drama that we see here.