Jules, apparently, they're not too worried about it. I've tried to get my sister to weigh in and she hasn't. Maybe that means she isn't worried about my ability to be situationally appropriate these days LOL. Also, my mom says my sister keeps saying that this is going to he relaxed, and she & my mom are going to have fun planning it.
Greyscale, I've attended service at this church in the past, and it actually is pretty relaxed. I wore jeans and didn't stand out. I think my sister even tried on a strapless dress, but she nixed it because of her need for a supportive bra. So bare arms or shoulders should be ok.
Sal, my mom said buy black pants (I seriously think she wants me in Palazzo pants the way she kept talking about this flowy pants that are so popular right now LOL), and she reminded me that my sister isn't a fan of many colors in her own home/wardrobe. I think I'm probably safe in pretty much any shade of blue on top without shocking my sister's neutral color sensibilities
Adela & Summer, I love what runcarla wore! She looked so relaxed without looking relaxed, if that makes sense. Also, it was very elegant. And if that's what I wind up with, at least it will be something I love enough to keep around for any future events or just to make me smile when I see it hanging in my closet.
Brooklyn, I'm about to cry again! It's not a bad cry. I just think it's so beautiful that your mom walked you down the aisle, and my mom is walking my sister.