at 'legend' !!!
I can certainly understand your need for sleep, kitty - but tiredness will absolutely not affect your milk supply! I posted a link to a paper that showed this the other day. Will find it later and post it in a minute. There is no reason why tiredness would affect the physiological process of milk production, any more than being tired affects your ability to breathe, or make blood, or lymph, or to perform any other normal physiological function. The study I posted showed this in practice - mothers' mood and fatigue did not affect production.
But you need to sleep to feel better and more energised, and every mother of twins, especially, should try to get help to have a break. Is there anyone who could take the dts out for an hour once a day for the present? How about a teenager or a student you know and trust, off school/Uni for the hols, who would wheel them out and about for an hour each afternoon for a fiver? That would be money well spent!! The fact you know you have an hour off will boost your energies in itself What about neighbours or friends who have offered to help? Maybe you can take them up on that offer. Some people would be thrilled to be asked, believe me - they would (rightly) think of it as a special treat to have your twins to parade around with
There is no point (IMO) in trying to hurry your twins' ability to sleep through the night. This is something you cannot engineer while they are this young, so do whatever you need to do for the most sleep for you - if that means feeding them together, then that's what you can do. Look after your needs for sleep and rest at the moment, and think about supprting them going through the night at a later stage, when they are not so new and you are not so knackered. If it saves you time, then maybe your dp can give one of them some ebm in the night ( but obv not if it is quicker to feed them together).
If you leave too long a gap between feeding (or expressing) then you will make less milk - there is no getting away from that, it's biology It's the frequency of feeding that drives the supply. If you use that 11 pm feed to give the twins formula only, then you are extending the gap between feeds to make it longer than your babies would leave it naturally - giving your body the wrong message.
You could think about topping up with formula at 11 pm to try to lengthen their sleep, but to be honest, I think this will have its downside - you are then messin' about with formula and bottles which adds to the hassle. It's up to you - maybe it's worth it to get another hour sleep. You have already intro'd formula so the exclusiveness of bf is no longer an issue....it's all a question of what works best for you, and what preserves your choice to breastfeed, and too much formula won't preserve that choice.
Over to you