Hi there and congrats on the twins! Isn't it interesting how HV vary - mine told me to stay away from hungry baby formula! Hungry baby formula can be really harsh on little tummies as it is made to be harder to digest so they feel fuller for longer. It sounds to me like they are doing well, my DD was all over the place with feeds at 4 weeks old and nights sound about right for their age too. I would probably start the day at the 6am feed to get the EASY pattern going in daylight hours and get the calories in during the day. Are you cluster feeding towards the end of the day and doing a dreamfeed or waiting for them to wake? What weight were they born at - I know my DD has had weeks of more weight gain than other weeks and it all seems to even out in the end.
What is their total formula intake over 24 hours? They are supposed to take 2-2.5 oz per lb of body weight although that is a rough guide, some take more, some less. Does it take an hour to feed them at every feed? Is that both babies each taking an hour or an hour one after the other? If its each baby that is quite a long time, especially as 1 hour is all the awake time they can probably handle - it may be worth trying the next size teat or a variflow teat (depending on what bottles you are using) to see if that helps.
Has your HV suggested you correct their ages? Just curious as I've never known them correct when babies are born from full term at 37 weeks!
HTH!
Laura