As I see it if I were sitting on a jury hearing this case it comes down to these questions.
1. Was Barbra mentally capable of consent/aware of what was happing?
2. If yes to one did she consent? ( as horrible as that thought is)
3. Is Chris fully capable of discerning that what he did was wrong?
4. To what level is Chris capable of understanding consent and incest?
If the answer to one is no then Chris goes away, whether he goes to prison or the state fruit and nut factory really depends on the answers to questions three and four. I really don't want to think about what yes to one and two would mean, that would be beyond fucked up, but I don't think I could in good conscious put either of them away in that case, fines, community service for Chris, and separate living arrangements. In that case they would be freaks, but adult consenting freaks. If he forced himself on her in any way he needs to go away for as long as possible but without a report from a psychologist I don't know where I would send him.
1) He admits to roofying her with ambien in his conversation with Null
2) Obviously not, and incest is a crime regardless of whether the parties provided consent.
3) Probably? I'd say at least partially; he certainly knew the incest was wrong, but I'm not sure if he fully realized/internalized that putting your dick in a doped-up senile person is rape.
4) Consent, not sure. It's hard to get as far as raping someone
without having a totally backwards view of consent. But considering how much he beat around the bush about who his "girlfriend," was with Null, he definitely seems to know that incest is wrong.
There are technically two ways a defense can plead insanity-- it can actually be applied to guilty
or not guilty. Given that Chris doesn't have any money, they'll probably have to take a guilty plea deal, so I'm going to put my money on "guilty but insane or mentally ill." When insanity comes into play, not-guilty and guilty are functionally identical, because they're pretty much going to get committed either way. Chris definitely qualifies for an insanity defense; even setting aside the autism, he's said in writing that he sees things that aren't there, believes himself to be the god on an alternate dimension, and cut his taint open with a knife because he thought labia were "growing" inside of him. He might not be too insane to discern right from wrong, but there's no doubt that he's insane in
some capacity.