When I tell you that trying to feed them at the same time is a disaster, I'm not kidding. But, then that little lightbulb goes off and you think you're a genius. You're not, you've just had more sleep that day than previous days..
Step 1: Get a boppy. 2 if you can, but one will suffice.
Step 2: Please the boppy to the side of you, whichever is your dominant hand so the open part of the ring is facing you.
Step 3: Put 1 kid in the boppy leaning the head against the middle of the ring so they are slightly upright.
Step 4: Sit up against a pillow, wall, etc so you are upright and place your other child on your lap with your knees up so they are upright.
Step 5: While making sure both kids are within arms reach, feed. You don't have to hold either kid, they are being help upright by either the boppy or your knees which will help with swallowing and digestion and you can feed both at the same time.
If your first question is about burping after, well that goes to another lesson you're going to learn. Well, more like your twins are going to learn: You won't always be first and you won't always be last. Burping at the same time is ok, but I found you were never really able to get a good one because of the lack of control. So pick one up, burp them, put them upright on the boppy or the bouncy seat and then burp the other one.
Once you've mastered this, you will drastically cut down on the feeding time for each kid and you have more time between feedings.