Others, such as elephants usually have only one baby to nurse.
Human mothers can nurse twins successfully.
It does take dedication. When infants are well established at nursing, some women may find that it works very well to nurse both the babies simultaneously, one on each breast. This is very difficult in the first weeks of breastfeeding because the babies tend not to stay latched on. Just as a mother gets one baby latched on the other one falls off. Another pair of hands is needed.