I am glad to see they've listened OP.
BUT
I must add my voice to the others saying you should be wary of promising to still be a bride's maid at this wedding though, baby with you or not.
There are women who pop a baby out no trouble and are back in their skinny jeans a week later. Looking glam and traveling around with ease. Personally i have never met one.
The chances are you may still be bleeding quite heavily, bruised down there quite heavily, leaking milk at the mere thought of your baby crying, suffering from back pain and lack of sleep or any time to yourself, be weepy and hormonal, and, at 2/3 weeks post birth, still be heavier than post preg. and still look roughly 6 months pregnant.
All this is not going to sit well with being dressed in a posh dress, expected to follow an excited bride around all day, stand behind her at the ceremony, be on hand for photos every few minutes, and generally spend the day looking jolly.
Sorry for sounding a kill joy OP, but having had 4 DCs i know what it's like. I didn't even manage to get out of the house as far as Tesco for the first 2 weeks last time.
It's all so worth it though. After the first couple of months you will be yourself again :) 