Divorce process in Italy

CALIFORNIA: I'm an American (living in CA) who is involved with a married Italian citizen. We have been together for 12 years and have two children (10 years & 8 years old) together. He has been married (in Italy) for 20+ years and also has two adult children (21 years & 25 years) who still live at home in Italy. He's been working onboard a cruise line for approx. 19 years and spends 6 months working at sea, with 2 months vacation between each 6 month contract.,

We are now ready to make our relationship permanent and he will need to file for divorce in Italy. Can anyone outline or adivse on steps that need to be taken in order to begin this process in Italy? Does the fact that we have two children who are U.S. citizens factor into possible legal residency here in the U.S.?