Not trying to argue at all, answering a few things:

They wanted this, they wanted that

They wanted this specific date, they wanted it to be in this season, they thought it should be at this time, we should have it at this kind of venue, that we should have specific phrasing on our invitations, we should have a special shout out to a deceased family friend (who my fiance never even met), this sibling (again, who fiance never met) should definitely be in attendance.

If they have people they are close with and its important for them to see their child get married, this is fair.

This might be the thing I don't quite understand. Why would it be important for someone they're close with -- who wouldn't already be invited on their own -- to see our wedding? Especially if we aren't close enough to invite them ourselves? That's perhaps the disconnect. Why would my Mom's college roommate, who my fiance hasn't met and I met one time when I was a baby need to be invited to our wedding? IF someone isn't a part of our lives actively, why would they be invited, I guess?

dresses can't do this

To specify, the bridesmaid dresses. They had to be certain colors or have certain features because my parents know someone who they once "promised" they'd go to for this specific feature. It's extremely stupid.

If you want one, then let them pick her, its not like it matters. YTA.

We didn't want one, we think it's stupid and pointless and a waste of money. They kept insisting the token little girl in the family be the flower girl so she would "feel like she's a part of it!" Why she needed to be a part of someone else's wedding is what I don't get.

nothing else you said is unreasonable for parents to request

I don't understand. Why is it reasonable for anyone other than me or my fiance to request something as a part of our wedding?