Need help legally, so that I can save my brother frm trap by girl

Sir/Madam, Please guide me on below family matter: My brother is planning to get married to a girl,which my family did not like.We know that the girl is liking/using her because of our family status/property/Investments. We tried to convince him through the actions/behavior etc shown by the girl that she is not fit for him.. but no luck. My bother is not listening to any of our talks,he is creating scenes at home. We talked to the girl & her parents to remain away from my brother,But her Parents have threaten us that they will do a FIR if we interfere as both are mature or if we do any harm to the girl. Even after all this drama,We came to know that my brother & that girl are constantly in touch (meeting, phone call,whats app etc) What actions should we take legally as well as strategically , so that I can save my brother from the trap laid down by the girl & her parents. Should we allow him to get married & before marriage we separate him from Family properties.(Most of the investments/properties are joint ) If you need more details ,please email me or call me. Regards, Sudeep