How to divorce a illegal immigrant?

I have a friend that is married to a illegal immigrant in Arizona. they live in a house together. there i s one kid on the way that is his and a kid that she already had when they got together. He is curious about divorce because of issues between them. He is curious if she will be deported, about alimony, and about the child. also is he at risk of any legal trouble for her being illegal. i appreciate any info.