I love photographing twins.  Some photographers think of it as extra work but I love having a spare baby.  One twin crying?  That's ok, just pass me the other until we're good to go again. 
I also find that when they are together they settle each other so well.  They're so used to being together in the womb that they love being close.

That was exactly the case with Jacob and Imogen when I met them and their mum and dad a few weeks ago.