The positions of your babies in utero will help determine if a vaginal birth is possible. As your due date gets closer, your care provider will be looking to see if Baby A (the baby closest to your cervix) is in a vertex position (head down). If Baby A is, then trying for a vaginal labor should be possible. If Baby A is breech (feet or bum first) or transverse (sideways) then you'll most likely be scheduled for a cesarian.
Baby B ends up being a little bit of a toss up. Even if Baby B is breech or transverse, your care provider may still agree to try for a vaginal birth. When you chose your care provider, make sure to talk to them about their experience repositioning babies. Many care providers who have experience delivering multiples are skilled in external version which is when a care provider presses on the mother's abdomen to move the baby with guidance from an ultrasound.
When you have more than two babies, positioning can get a little more complicated. Again, it all comes down to Baby A to get the ball rolling but as you have more babies to get into ideal positions, you may run into some complications that will require a c-section in the end. However, if your care provider is skilled in external version, Baby A is head down, and they and think you're a candidate to try for a vaginal delivery, then go for it.
There are many variables that must be taken into account with a multiple birth. Not only what was noted above, but also your health, how your babies are growing (one sac or two, separated or fused placentas, etc.), and many others. The above examines just one factor but be sure to have an open conversation with your care provider about what seems feasible given your unique situation.