This is hard, but it's going to be OK.
Current surgical techniques are so excellent that scarring and asymmetry is kept to an almost-invisible minimum. Because Baby will need a couple of surgeries in his first year, mom should consider reading up on ways to feed him breastmilk-- it has so many antibacterial properties and gasterointersinal-soothing qualities and those will both be vital for a baby who needs surgeries. Also, babies with clefts are prone to more ear infections because the tubes going from the back of the nose to the inner ears may not function properly. In "The Breastfeeding Answer Book," which is La Leche League's medical text, is says, "The muscles of the palate normally open the ear tubes during swallowing to equalize ear pressure. When these do not function adequately, fluid can accumulate in the middle ear and may become infected. In a study on babies with cleft defects, those on formula developed more ear infections than those receiving some human milk. The immunities in human milk provide protection against all kinds of infections, which is especially important when a baby is facing surgery." Babies can nurse or receive human milk within three hours of surgery, even when other foods and fluids are restricted, because it is so easily digested. This will help both mom and baby feel more at ease when they are facing surgeries.
Anything Mom can do to reduce the chance of infection is so, so valuable, and will also help her feel more connected to him even when medical staff must help with his care.
If the cleft is only in the lip and is unilateral (one side only), mom may be able to help baby maintain suction at the breast by positioning the nipple to one side of the cleft and using her thumb to fill in the space above his upper lip. An IBCLC-certified lactation consultant can demonstrate the "dancer's hand" position which can help support Baby's jaw and chin, if needed.
If the palate is involved, which is likely, he will probably not be able to maintain a proper latch to breastfeed. Feeding can take longer than with a typical baby. It will probably take most of Baby's waking hours to feed him during the first few weeks. If mom is prepared for this and well-supported, it can be a sweet, bonding time. If she is worried about other children or preparing meals and doing chores for herself and other family members, she may feel discouraged and frazzled. Extra help is nice for all moms, but an absolute necessity for a mom who is helping a baby who has a cleft. If she will be having a baby shower or blessingway party, consider having a sign-up sheet or calendar so people can volunteer to help with meals or laundry, and make sure Dad knows his help will be needed a lot.
Consider using a Breck or Haberman feeder or other device that does not depend on suction to offer milk--a Haberman will not "flood" a baby, which would cause a baby with a cleft to choke and cough and get frustrated and not get enough.
Many surgeons will install a palatal obturator. It's a plastic plate that is placed over the opening of the palate and shaped to cover it. Obturators are used before palate surgery to close the gap but prevent the baby's hard palate from closing in an improper way. It may be fitted as early as 24 horus after birth or several weeks after birth. Baby's mom should tell the baby's plastic surgeon she would prefer a smooth (rather than a rough) palatal obturator to faciliate comfortable breastfeeding. Later speech develpment is greatly aided by helping the baby develop normal sucking patterns.
Mom will probably need an excellent breast pump to establish and maintain her milk supply. A hospital-grade rental pump will be the most effective option. This would be a great group gift for friend and family to chip-in on.
Finally, it's nice to have a few cute clothes and/or booties and hats for mom and dad to enjoy putting on baby. That's true for all babies, but especially true for babies with any kind of atypical physical appearance; parents need every opportunity to see their babies as the darlings they are so they have positive feelings towards their babies and can support and comfort them well through surgeries and/or feeding challenges. It can be useful to have some baby gowns that are open at the bottom (as opposed to footed) so if medical staff needs to attach monitors to Baby, his feet and tummy can be easily accessed.
Please consider reading more about cleft issues at www.llli.org. That's La Leche League's main site, and it will have many helpful and positive stories from mothers who have been through this. Consider contacting your local LLL Leader for support and information both before and after Baby arrives, and also consider making an appointment (even before Baby comes) with an IBCLC-certified lactation consultant. There will likely be at least one on staff at a hospital; part of their training specifically relates to helping mothers whose babies need extra help. An IBCLC-certified lactation consultant at the hospital where Baby's surgeries will be performed are likely to have cleft-specific experience.
If you'd like to send a small gift, consider the booklets "Nursing Your Baby with a Cleft Palate or Cleft Lip" by S. Danner and E. Cerutti and "Give Us a Little Time: How Babies with a Cleft Lip or Cleft Palate Can Be Breastfed" by C. Herzog-Isler and K. Honigmann. I know the second one is available from LLL online; I could try to help you find the first one if it is not easily available from LLL online. These booklets have many photos of babies before and after surgeries, which can be both comforting and disconcerting for parents. Still, I recommend then because they show these babies first and foremost as babies like any others who are ready to love and connect with their families and need lots of support to get through their difficulties.
My sincerest best wishes to you, your sister's family, and your darling nephew, who will probably amaze us all at what a tough but sweet cookie he is. What a great, supportive auntie you are!