Congratulations, twins are fab!
My twins were delivered at 34 + 4, the reason being IUGR, so there was a bit of an intake of breath when Twin 1 came out as he was 5lb 1 oz and they weren't expecting him to be that big. Twin 2 was 3lb 14oz, so was considerably smaller, although needed less support than his brother. He soon caught up weight wise though and is now the taller of the two.
They went to SCBU into oxygen for the first 24hrs, then were in normal cots in scbu. They were tube fed due to being born before the sucking reflex has developed, but I expressed and we got breastfeeding established before they left. They spent 2 weeks in SCBU.
They are now thriving 8 year olds. They are middle ability at school. In hindsight I think they would have benefited from starting school with the next year group, but it was not possible to do that at our school in that year. Given that your twins would be born in September if they had gone to full term, you have a good case for arguing that they should be in the next school year down if that is a route you want to take. I do feel that mine are less emotionally mature than their classmates, but other than that they are fine.
One other thing to note - when you go into theatre, there are LOADS of people in there as there is a team of medics for each baby (I had an emergency CS with my first and it was really noticeable how many more people were in theatre for the twins).
Looking at my boys now compared to their friends, you'd have no idea that they had been early and they hit all milestones as and when they should, so please try not to worry.