I've read a couple, but I really haven't found a multiples one that I really like to be honest. The two multiple pregnancy ones I have are
Twins! by Agnes, Klein and Ganon
When you're expecting twins, triplets or quads by Luke and Eberlein
which I've read in addition to all the zillion single pregnancy ones (what to expect, girlfriend's guide, etc).. They aren't bad, they just weren't as comprehensive as I would like.
one book I have really found I like is called Juggling Twins by Regan-Loomis but it is more focused on taking care of the twins and not the pregnancy itself
sorry this may not help much, but some ideas to check out if you're in a bookstore =)