Along with a DNA test I would HIGHLY recommend a STD test and maybe try using this new thing called a CONDOM??? . "Potentially" having 5 children may be the least of his worries.Does Mike have an attorney? If not he needs one yesterday. This attorney can find out if the husband is still legally considered the father.... DNA that does not match his does not automatically make him not their father legally.
If they no longer have a legal father... Mike needs to get DNA tests done on all 5 children to establish his paternity.
She has filed for child support.
He can file for custody and visitation of ones who are his children. Most likely he will get joint legal custody with the mother, some visitation and have to pay about half his income in child support, transportation costs for the kids to visit him, etc.
He can start out trying for full custody since she no longer has the children.. it might work. But I think his chances are slim. He can expect to pay a lot in legal fees for all this.
Keep in mind that you are a legal stranger in this case... you have NOTHING to do with it.
So most people here will not give you legal advice. If Mike would come here for advice he might get some help (but you might want to suggest to him that bad mouthing the mother of his children will not fly here. He is the one who choose her for the mother of his children. He’s stuck with her for the rest of his life.) You can give him moral support, but you cannot do this for him. He needs to be the one doing everything for the case and for his children. If he wants to now start being a parent he really needs to structure his life around his 5 children. And 5 children are a lot of children for anyone today.
If he gets visitation you will be the step mom of what are probably very disturbed children. This is really going to be hard on you on many levels... You already have a very nasty attitude about their mother, you have already decided that the child with a disability does not have a disability even though you have no clue and have never seen this child. All of this will make it very hard to be a step-parent to these children. They will resent you to no end just because you are the step parent. Kids just do that with step parents.
You really do need to think about this long and hard... do you really want to be married to a man who is paying half his income to 5 children and have your future child's life disturbed by 5 high need children? In marrying you he will be getting a free baby sitter and house keeper. Your future children will be losing their mother even before they are born.
Your responsibility is to your children, not to his and the other woman’s children. All of the problems that those children bring into your home will become your children's problems.. the drug use, the abuse, the neglect, the rough life... all of it. You will be short changing your children in so many ways it’s hard to even start to list them.