First of all, it is your wife who is the parent and they are her kids and this is her case.
I don't know that you have enough actual proof of the things you accuse Dad of doing and being. That would depend upon Iowa law, and your wife would need to discuss the voice message on MP3 and the convicted child rapist issues with an attorney. Did she file any reports or motions at the time the rapist was living with Dad and SM?
What has Mom done, legally, about the claims of abuse by the son of Dad's roommate/gf? Proof that he lives there is not proof of molestation.
Visitation is a right -- Dad does not have to use his visitation. That is not a crime.
How Dad makes his living is none of your business. If he's on disability, then that is how he supports himself.
Involving yourself in his personal business, such as insurance claims, does NOT help the coparenting relationship between Mom and Dad, does it?
I don't know what Mom's chances are at supervised visitation. That depends in part on the answers to my (and others') questions, and also upon the judge and many other factors.