Jen - I'm so sorry to hear about what you are going thru, and with two small children. Interesting, I am going to recommend the same firm as the first person - I went thru Maureen Sullivan Taylor ###-###-####, and it all went as smoothly and inexpensively as I think is possible.
My first husband was an a-hole, cheated on me, etc., but we didn't have any kids. I have a great husband of almost 6 years now, and we have beautiful twins, too. Life is short, and you should be happy. You're young, and there's much ahead for you. It will be hard to be on your own with children, but if it's the right thing to do, then don't feel bad. You're not the one that did the cheating, and if you can't make it work, then move ahead to better things.
Also, if you haven't already, make sure that you belong to a twins' club. The members should be a great support to you along the way. There are numerous clubs in the area, one of which is www.wcmotc.com.
Good luck!