For the situation where one twin was 5+ lbs and discharged home while the
other was 2+ lbs and remained hospitalized:

I would be sure that this new mother gets a good, electric breast pump with
double pumping setup, and starts a regular pumping regimen as soon as
possible, so that she can build a milk supply for 2 babies.  Even if she
does not nurse long-term, she should know how beneficial her milk is for
the welfare of both her babies right now.  Her hospitalized baby may be
very sick at this point.  Her milk can diminish the risk of that baby
developing such complications as necrotizing enterocolitis.  Kangaroo care
can also help stabilize this baby's temperature, as well as enhancing her
own milk ejection reflex (as explained so interestingly by researcher
Kersten Uvnas-Moberg, MD, PhD at the ILCA conference in New Orleans in
August) through skin-to-skin contact.  Others have already posted about the
protection against germs in the environment through the mother's own milk,
as she passes her antibodies on to the baby.  This depends on her sharing
the environment with her babies.  It won't work if she doesn't get exposed
to the same germs as each of her babies.

While the mother may bond first with the more vulnerable, hospitalized
twin, it is also common to bond first with the healthier baby who is at
home, and to unconsciously view the sicker baby as an intruder on that
relationship when s/he comes home later.  It is also a protective defense
to not get too attached to a very sick baby, in case the baby does not
survive.

I'd give this mom all the caring and support possible during this difficult
time for her. This would include a chance for her to talk about how she is
feeling, how hard this is, as well as practical helps like transportation
back and forth, cooked meals, household help, etc.  If the bigger baby can
visit along with mom, it would be great to have you, or another helpful
adult along, to hold and care for this baby while mom learns to breastfeed
or kangaroo care the hospitalized baby.  Lots of times twins, especially
identical ones, do settle better together, though the hospital may not be
willing to allow it at this stage.

A final note: there are some great lactation consultants in the
Philadelphia area, such as Kay Hoover, who may be able to help directly or
recommend a colleague at that hospital.

Anne Altshuler, RN, MS, IBCLC