when I nursed my twins at the same time it was always referred to as tandem nursing by NICU staff, pediatrician, nurses, and lactation consultants.
Here's what wikipedia says:
Feeding two children at the same time is called tandem breastfeeding The most common reason for tandem breastfeeding is the birth of twins, although women with closely spaced children can and do continue to nurse the older as well as the younger. As the appetite and feeding habits of each baby may not be the same, this could mean feeding each according to their own individual needs, and can also include breastfeeding them together, one on each breast.
at 11:28 PM on Sep. 12, 2010