How to catch this person in a dating scam wanting money?

Our brother met her on ChristianMingle.com. He has been drug into this love relationship but they are demanding more and more money. He doesn't have any and is in very critical health. We have contacted everyone we know and no answers yet. She [?] is also scamming another guy that we found out as of a few days ago. This site is trying they say to stop them.