okay as somone about 2 weeks away from having a child, I can understand not wanting tons of people at once in the hospital. Our parents have requested calls no matter what time it is-my DH's parents will not be here (our entire family lives on the west coast). However all my girlfriends from work plan to stop by the hospital and I will be happy for some adult time and visitors.
your SIL sounds like a bitch and this whole I need to bond with the baby, yes so does everyone else. That bonding thing is really only discussed for the first couple of hours when the baby comes out when you are trying to get the BF thing going on.
Anyway, as far as the shower, its actually against ettiquette that the family throws the shower because its like the family asking for gifts, friends are supposed to throw it.
I think someone else asked this, but is your SIL young, she sounds very immature.
I bet your Bro and SIL will be more than happy to ask your parents to babysit, so why the rudeness now, I think you might want to speak to your brother and give him a heads up how much your parents were hurt by their behavior and as your parents go, you should encourage them to be honest with your brother and let him know they will not be taken advantage of.