G.W.
Wow, you are a busy busy lady! I have twin boys who are seven. They were the biggest surprise of my life and at first I was not happy about an unplanned member of the family (we were trying to get pregnant with ONE more, not two!) but they have turned out to be such an amazing joy and huge blessing to us as parents and their older sister.
People used to (and sometimes still do) say "I don't know how you do/did it". That always makes me smile because I want to respond, what else would I have done? Let one starve to death or let one sit in poopy diapers all day??? LOL The bottom line is (and I suspect you already know this!) that you do what has to be done. You feed two, you change two....all day long :-)
My advice is schedule schedule schedule. And whatever one does, the other does it too. For example, I always made sure they both finished bottles. My friend was feeding one when they were infants and she let him stop because he seemed like he was done. I said, "No way, you put that bottle back in his mouth. If he doesn't finish, he will be hungry in two hours and then I'm feeding all day long, back and forth". So if one woke up for night time feeding and I got done and the other one had not woken up yet, I woke him up to feed. No way did I want to lay back down only to hear a second cry 45 minutes later. I made sure they always napped at the same time, too. Never let one sleep without the other or I would have never had a moment's peace.
Mine slept in the same crib until about 4 months old and then we separated them. They went into their bed the first night we brought them home, I know its a personal choice but we are totally not into co-sleeping.
When they started spoon feeding, I fixed one big bowl of food and fed them both from it with the same spoon, what's a little germs between brother's right? :-)
Hopefully you will have lots of help with the older sibs and your family. My husband helped when he could but I tried not to make him do too much in the night since he did have to work. God was very merciful to us, I only remember 3-5 times both of my boys were awake at the exact same time in the middle of the night ready to eat.
Congratulations on your upcoming twin birth. I promise you will survive!