Of course you're right.

So, what can we do in the meantime?

He went to GF's home last night while her 16 year old son was home alone. He was drunk and high yelling and screaming. Wanted to know where GF's BIL was because he thinks he's involved in the conspiracy.

GF, parents, sister and BIL all rushed to the house and he left. I called him and asked him to meet me. For some reason, I'm the only one he would take a call from.

We met and he was clearly agitated as well as drunk and high. My goal was to diffuse the situation by showing sympathy. As well, I encouraged to think about what he should to about his predicament. He came to the conclusion that he should hire a PI which I encouraged. My thinking was that if he followed through in constructive ways, rather than destructive ways, maybe he'll come to his senses while leaving his family members alone.

Should I continue to encourage this? Should I tell him he is wrong?

What about interventions? What about consulting a psychiatrist or a rehab facility?

I'm too new to post links but there is a Dr Phil episode that covers this very topic. He got the man to admit that a disorder could be just as plausible as a conspiracy, thus, he was able to get him to seek help. Our situation is different in that bro isn't seeking help from anyone let alone Dr Phil.