I know this is crazy. You have two miniature humans growing inside your body. It's fucking WEIRD.
So it's totally reasonable to be overwhelmed. It's ok to want to kill everyone. I don't blame you. In fact, if you asked, I'd probably help you commit the necessary murders.
Here's what you need to do:
Tell your family to lay off. Tell them you're tired/stressed/in a murderous rage and they might not survive the day. In the absence of that option (which is often easier said than done) tell your husband to come to your goddam rescue for once and hit them over the back of the head with his hockey stick.
Next, escape whenever the opportunity arises. Go to the bathroom (ie, surf twitter). Go have a nap (ie, surf facebook). Hell, go for smoke outside if it will shut them up. And when you can't escape, sit quietly in a corner and make people come to you. With your dog at your feet as a guard/ankle biter.
Finally, call you friends. Friends are just better than family. Sorry, but we're WAY less annoying. We'll come clean your kitchen while you watch tv. We'll make you tea without expecting you to chit-chat. We'll watch soap operas in silence. We'll walk the dog. We'll help you launder new baby clothes and fold them neatly in little stacks in the nursery.
And when the little munchkins finally arrive, we'll change their diapers for you. And we'll watch them while you nap. And we'll take you out for lunch when you need a break. We'll babysit if you want to leave the effing house already. We'll bring you flowers on a bad day.
Ultimately, we'll do all these things without annoying the shit out of you. We'll do it because you need it, not because we have some insane need to be involved. We'll do it for YOU, not for us. And we'll be happy to. We'll leave you the eff alone when you need it, and all you'll have to say is "I need some space". We'll butt out. But we'll be there.
Oh, and one more thing, don't forget: everything will be fine. Those little buggers are going to join you soon and it will all be a glorious happy time. And you'll have your strength and sarcasm to get you through.
Oh! And the presents! Bask in the glow of all your presents. That will help.