J.B.
Hi L.! Congratulations on your twin pregnancy!! I also have twins, age 28 months, and if I recall, it is normal for them to be somewhat different sizes (think about how full-term babies are different sizes). As as Erin said, the Saddleback Mothers of Multiples Club is a great resource. I joined as soon as I found out I was pregnant, and have found it to be a wonderful group of women who have helped me immensely. Check out www.smomc.org for more info; you can register on the site and someone will call or email you to help you get acquainted with the club.
Good luck!!