Congratulations to your sister! And then are officially will be an 'Aunt', how wonderful that is with double blessing! My husband and I have gone on 4 years of trying to get pregnant too with clomid, ICSI, and then IVF with egg donor. So, I know what it is like for your sister to go through too.
The 'baby' market has changed so much in the last 5 years since my twins' were born. When I see new strollers for twins I say, How I wish I had that?!
1) They'll be natural at what they do!
2) Keep a note pad to stay on schedule
3) 2 Boppy pillows (are great to use when feeding)
4) Take turns with night schedule (for example; I get up for 2 AM feeding while my husband get up at 4-5 AM and then get ready for work)
5) There no really need to buy TONS of clothes beginning of the first 6 months. That because we brought tons of (gifts) were bibs that my twins' wear all the time so it doesn't get onto their onesies. Because they grow so fast in the first 6 months. We had a couple new cute outfits but they were not out in public the first 6 months because I was in fear of other people / strangers touching my babies.
6) Get those donut holes for bottle fed when they are around 6 months old they will start learning quickly on how to hold their OWN bottles with their hands than most singular babies.
7) I don't know how she would decide but we had the twins' sleeping in the share crib for first 3 months and that when we separate them and learn how to sleep at night for the better
8) Biggest mistake that most mothers do is pick them up when they cry because eventually it'll be a pattern same as rocking chair. We used to just touch their hands give them a gently touch on their face to sooth with music it work for us--may not always work for others?!
We had it very easy than most of my twins' group (I am an organizer for the twins consistent of 38 Mothers). We are really fortunate with that and we never gotten ANY help. It was rough I say but we managed and made it!
The things she will need for now is--
1) Double strollers with infant seats
2) BPA bottles (there are so many out there and its really depends on her twins' with 'nipples'. We tried out 4 different ones and found 1 of them to work for us. Can you imagine twins' are picky on which bottle to use?!
3) Bibs
4) stock up diapers (We love the Pampers for newborn, Stage 1, 2, 3, and then we got the Target brand diapers they work well to save $) doesn't matter just buy them every month and pile them up in the garage/storage.
5) Wipes, Wipes, Wipes
6) A lot of ointments!
7) 2 of the bouncy rockers from F/P (there are so many) but it work for us.
everything else can WAIT and decide which one to get (we never had 2 the same of everything we had 1 extrasaucer and 1 jumperoo (that is a MUST to buy) we had them take turn and they like it..
And lastly I had mine at 37-1/2 week with c-section due to high blood pressure to save me and then had Preeclampsia after the birth almost literally died that day. But I am here and doing well!
PS. I finally FOUND the site that has donut holes (they called it now 'Bottle snuggles') It used to be a ring with hole in the middle with bean but I guess they changed it. Here the site 'www.bottlesnugglers.com' it made our life easier when you are breastfeeding (I couldn't do both at the same time) so I had pump one and use the snugglers for one and then next round it would be my other set of twin to do bottle/alternating it.