Congratulations!
We had DS1 (2 years, 2 months) when the DTs were born, very premature at 28 weeks. They were in NICU/SCBU for 3 and 4 months, so we all had a pretty hard time. DS1 was potty trained in intensive care units!
The DTs are now 7.5 months and fab.
Some-one said to me, when we found out that I was expecting twins at 7 weeks (bleeding - this is starting to so sound like Jellibob's tale of woe, but not meant to) "Don't worry, you'll deal with it". That was the best thing that any-one could have said. There is no way that I was going to spend years of my life "just dealing with it", I decided that I was jolly well going to enjoy it. And I am. Wine helps .
I find it helps to say loudly to the DTs that it's DS1's time now, to counteract all the times I have to say to him that I'm doing something for the DTs. Also a big fan of routine - the first time that I got all 3 to have a lunchtime sleep at the same time was a moment of great pride and joy. I also ask DS1 if it's ok for the DTs to impinge on his special time, for example, "is it ok for the DTs to listen to your story too?"
We have an icandy pear for the DTs and DS1 walks, unless we're going out for the day all together with DH, and then we take a pushchair for DS1, but mostly use it to carry picnic/flask etc.
I can't imagine having DS1 and just one baby, it seems normal to have DTs.
The other handy thing is that the DTs are endlessly entertained by DS1.
Am I rambling? Perhaps it's the wine...