If he is filing the FAFSA now, he would put down divorced, because that is his status if he were to file today. Yes, he will use his 2015 income, but he will separate his income from his ex-wife’s and put only his 2015 on the FAFSA in the student income section. Since he is now a dependent student, your income/assets as his parents will go on the fafsa.
He should probably still order a transcript of his tax return from the IRS. HE will need to submit this along with his own W-2 forms.