Hi there. I'm the other half of the rambling twin mum. Much of what I'm about to say feels a tad delicate, but hopefully you can read between the lines of some of it. The content of my advice for my pre-paternal self seems like it is centred around damage limitation - and it sort of is to some degree - but when you look back on the most surreal phase of your life it somehow doesn't seem as bad.
With the pregnancy and birth side of things, I'm not sure I have much more to offer than what has already been said. To be honest, at this point, none of your work has really started yet. I found the pregnancy phase quite fun. There is the obvious excitement, the opportunity to make an unoriginal but still hilarious joke about your wife's figure, the insincere sympathy and the unsuccessful efforts to make her feel comfortable. With the birth, try not to get too excited too early as it takes a while. There is a lot of sitting around, broken up by the occasional fetching of a drink etc. And even though you may have spent the last three nights sleeping in a chair, the effect that this has had on your lower back is not something worth discussing in the delivery suite.
After the birth
This is the time when you're really winging it. But you mustn't let it show, especially with twins when you have nowhere to hide. You somehow have to find the right balance between following you're wife's instructions (usually to the letter) and thinking proactively of what needs doing next. A trap I think men can easily fall into is to never be the one to suggest an idea, and assume that intrinsic maternal knowledge trumps anything you have to offer by some distance. The truth is that your wife is as new and clueless to a lot of things as you are. And in some instances, she will perhaps feel more pressure to find the solution because she ought to know. One of the things my wife has recently said to me (all through the lens of hindsight of course) is how much she appreciated me taking the lead on some things and assertively telling her what she needed to do at times when she couldn't think straight. But like I said, it is a balance, and a fine one at that.
Now this may come as a surprise to you, but your wife will be a tad more highly strung in the first few days and months... well pretty much the first year to be truthful. The trick is to not compare her current character traits to anything you have experienced from her previously. And reminding her of how 'fun loving' she used to be is not helpful. Similarly, taking personal offence to her tone of voice is something that is easily done in the heat of the moment (after all, does she not appreciate how hard I'm working, at work and at home? And does she not realise how I don't deserve to be spoken to like this?) But articulating these thoughts is not helpful. Not helpful at all.
To continue this theme, there will also be occasions when you are managing to perform a baby task in a manner that you believe to be perfectly acceptable. And it probably is. However, you are not doing it in the precise way in which your wife likes to do it. So, inevitably you get told you're doing it wrong. Now, at this point you have two choices. You can either suck it up, mumble an apology, and make a mediocre effort to follow what you now discover is a 'simple instruction'. Or you stick to your guns; you use your skills in logical reasoning to explain to your dearly beloved that there are alternative methods that could be employed here, and that if she in turn were to employ some lateral thinking, there could also be a whole number of other tasks that could be made more efficient with a few gentle tweaks in technique. I'm not saying that either of these approaches is the 'right one'. With the former, you run the risk of allowing a precedent to set in where you play the role of incapable incoherent 'man' in all such future scenarios (and uphold a stereotype that probably forms the number one topic in Mum to Mum conversations); and with the latter you lose. I'm not too sure how, but you definitely do. So the choice is yours. There probably is a middle-ground somewhere, but I'm not too sure if finding it will have any affect on the outcome.
With regards to baby care, you'll probably find that most of the jobs (nappy changing, bathing etc.) are not as difficult as you first thought. You'll think at some point that you could potentially do anything if only you could get some sleep. Twins tend to wake each other up, so be prepared for both of you to be up most of the night for the first few months. The other thing you'll find is that there will be a point when you become immune to the sound of babies crying. It will feel like you don't have enough hands to manage one baby, and because of this, the other one will probably be left crying for long periods of time. So blot it out, it's just noise. After all, what's the worst that could possibly happen?