write a simple letter explaining the situation and attach copy of his passport, marriage certificate, kids' birth certificate, H-1 visa number, F1 visa number, green card number, ssn, his new wife's name, address, birthday, a copy of his second marriage certificate (could get it from his local court house by giving just name) and other identification info. send the letter to US consulate and to his local BCIS office.
again, two marriage cerficates (new and old) are extremely important. If you could not get second marriage certificate, get some evidence of his new marriage such as wedding invitation, announcement, friend's statement under oath, wedding photos, etc. If he is not legally married again, you do not have a case in my view.
he is violating US law by having two wifes. If BCIS knows it. He could no longer get any visa or Green card or citizenship and is deportable.
if you fight on the US court for divorce, you might end up half of his asset plus alimony.