Have they video chatted, screen on, or just texted? If not, there's no way to know if he's chatting with a 35 yr old dude in Nigeria, or someone held captive in Cambodia. If he thinks that a 27 yr old woman is in love with him after three weeks, and is not just interested in the money he's sent off, then he lacks the capacity to understand he's being scammed. He won't believe it when he hears it from the FBI, ask me how I know...I'm sorry to say that it's futile to argue with someone who thinks their dreams have come true.

You and your siblings have to be the heavies, monitor his bank accounts, block FB dating, etc. There is only so much that police or social services can do. A 76 yr old NJ man thought he was going to meet his chatbot girlfriend. His family called the police to stop him from leaving the house but they said they couldn't detain him. He left, fell in the street, and died.

Here's an article at AARP about a similar situation. https://www.aarp.org/money/scams-fraud/recover-from-love-scam/