I agree with another user here (forgot username and cannot find post) about Chris not going to jail as soon as he's charged. He'll be charged with rape, incest, elder abuse and listed as a sex offender but he will receive a suspended sentence and spend X amount of years on parole, do community service, won't be able to live within a certain distance of schools or parks, but still living out in the real world. Whether he breaks his parole conditions, or does something else, which lands him in the clink is another story.
I imagine Barb will be put in some sort of assisted living facility and Chris would only be permitted supervised visits, if even permitted to visit at all. Perhaps any of her assets will be sold in order to pay for that, but what happens when neither a mother nor her son are capable of making decisions like that? Barb because she clearly has quite onset dementia, and Chris because he raped and abused her so there must be some sort of legal conflict of interest there. Who steps in? Will Joseph (Chris' half-brother) come onto the scene? I know that Joseph hates Barb, and by proxy Chris, but his own mother was raped by his estranged half-brother - it would be hard to not have that affect you.
All you need to have, to get someone arrested and questioned for any kind of sexual crime, is someone saying it happened. You need evidence to charge someone with the crime, but when you have messages and audio of the potential perp admitting to the crimes in question, then it's pretty open and shut. They will do a rape test on Barb, but unless they come across evidence that suggests that Chris was coerced into saying those things, I don't think the results of that will matter too much.