Oh mama, I know that well. I was so filled with anxiety before and after my girls were born. They spent 3 months in the NICU and I fought SO hard to get them home, when they finally arrived I went to pieces. This is totally not PC but I took Xanex for the first 5 days after they came home. I was so worried that I was crying all the time and had horrible nausea, I couldn't keep anything down. I normally NEVER take drugs, even for a headache but it was necessary for me in those first couple days. I also had my mom come stay with us for three days.
If you do not have any family around maybe consider hiring a nanny with multiples experience to help you for at least the last week before they arrive and two weeks after they are born. Even if you think you can handle it the noise level will get to you, I have become very comfortable with the sound of a crying baby! My daughters are 13 months and I still have a mother's helper come once or twice a week to give me a break.
There IS a light at the end of the tunnel, my girls were hard until about 9 months old and then it was like a light switch. All of a sudden they started to feed themselves, play, crawl and interact with each other. I will not lie to you, it is hard but also so much more fun then I could never have imagined. I have laughed more this year then any year before. My girls are SO much fun now and I have not had that horrible anxiety after the first month.
As for your living situation, it will be hard to have so many people in such a small space. Make sure you invest in a double stroller so you can get out of the house and not have to hold a baby for a little while. I also had the twin Moby wrap which was great for carrying both of them until they got to about 9 or 10lbs and then it was too much weight and not enough support so I switched to carrying one at a time in the Ergo.
Feel free to ask me any questions, I have been there and I can say I am finally on the other side :)