I think there are a couple of things that you need, but I would wait and see how things go before spending lots of money - we bought tons of stuff that we never actually used but were persuaded they were "must haves"!!
You'll need 2 car seats obviously
You'll also need a double buggy of some sort
Feeding - I don't agree that if your babies are small, you'll be advised to give formula top ups so you'll need bottles. You might want to have a couple of bottles just in case thats what you decide you want to do, my twins were tiny & in SCBU but formula was never recommended - just my experience but most SCBU staff are really pro breastfeeding so if you say thats what you want to do, they'll support you. I didn't use formula / bottles until they were over 6 months (definitely saved money!!).
Similarly, I wouldn't buy a pump to start with, most hospitals will lend you one and I think some NCTs have them too. I borrowed a Medela electric double pump from the hospital to start with and then hired one from a company online, and then after a couple of months used an Avent single hand held pump.
As everyone has said, just be open minded about it all, and go with the flow. I am an absolute believer in happy mum / happy babies so go with what works for all 3 of you. I did use a breastfeeding cushion though (just a Mothercare one - think it was £20).
Also used bouncy chairs - couldn't have done without 2 of those. Only had really cheap ones but they were fab.
Sleeping - we had moses baskets that they slept in downstairs during the day, took them upstairs at night and placed the moses baskets inside the cot bed. They used the moses baskets for about 5 months, then slept together in the cot bed (at either end) until they were 9 or 10 months I think and then we put them in separate cot beds.
Steriliser - bought an Avent steam one when we started using bottle but it was a faff so just used a large tupperware box (and lid) and Milton sterilising fluid.
Bought an Angel monitor - never used it the breathing sensor on it so would suggest that any normal monitor is OK.
Clothes - my twins didn't wear anything but babygrows for months, so don't buy lots of clothes. You'll get lots as gifts no doubt and they grow out of clothes so quickly.
It might be worth checking out the NCT website - they have Nearly New Sales and the quality of the things on sale is usually very good. We also have a local toddler group that has sales twice a year and similarly there are some good bargains to be had (cots / cotbeds etc where you can buy a new mattress etc).
Good luck - its so exciting!