Is a c-section always necessary with multiples?

No: Cesarean's are needed for certain positions of babies. Usually if there are three or more, at least one of the babies will be in the wrong position for a vaginal delivery. If the babies are early, a cesarean may be needed to protect the brain. However, if there are just two babies, close to term and they are both in the right position, a vaginal delivery may be possible. Talk to your doctor.

Needed no; advisable: 80% of all twins are born via c-section in the us nowadays. That is due to concern for the well-being of the second twin - 20% or more increase in perinatal mortality/birth injury compared to the first twin. So, to answer your question directly, it is not always necessary but it is always advisable to deliver twins via c-section. All higher order multiples (triplets or more) must have c-section!