For optimal fetal positioning with twins, use the same 3 Principles of Spinning Babies that you use for a single baby.
Manual cephalic version (when the doctor or midwife manipulates the baby into a head down position) is too risky for most twin breeches.
Bring your body into balance to allow the babies to wiggle into head down positions on their own. Most times this will be helpful when the mother works routinely on fetal positioning from the 2nd trimester, or early in the third trimester. Don't wait till a breech is known, the non-interventive techniques will not make a head down baby flip to breech. Keep the inversion short - 30 seconds is enough in the 2nd trimester no matter what the baby's position is.
When doing the forward leaning inversion for a KNOWN breech baby, increase inversion time from 30 seconds to 2 minutes and repeat the inversions up to 3 times a day. Keep it up until you feel your baby kicking in the top of your uterus, or your care provider determines that your baby is head down.
There are various reasons that a twin may become breech, including trying to fit the available room in the womb. Body balancing will increase available room by softening the broad ligament and reducing a twist that might be present in the lower uterine segment. Chiropractic adjustments can also help, especially when used with the Webster Maneuver. The forward-leaning inversion is a slower way towards the same goal.