<human>: Can you provide a brief rundown of the text in within 3 sentences?

Okay weddit, so I need some help with what to say :(

I've been friends with a set of four siblings for my whole life (3 sisters and one brother), and I've been meaning to ask the two eldest sisters who are closest to me in age, and therefore good friends with, to be my bridesmaids. The other eldest brother, youngest sister, and their parents are invited to the wedding as well as guests. Their brother is currently not in the same city, but he's getting an invite regardless of course.

So while the youngest sister is a truly lovely person and I love her company, I wasn't planning on asking her to be bridesmaid since we're not particularly close. I find out events about her life (getting into college, having a boyfriend, etc) through fb or through her sisters, and I'm pretty sure she finds out stuff about me the same way. Which is totally fine, we're a couple years apart so it happens. 

Anyway, so I'm having an engagement party in a few weeks (YAY!) and I've invited only the bridal party
<bot>: Asking 2/3 sisters to be bridesmaid, how do I let the last sister know she isn't in the party? :(