I never heard osmani brothers are worth that much, so far i heard its around 300-400 millions.
Their legitimate buisnesses is worth that, their casinos, construction companies etc. But they also own all the red light districts in Hamburg and are heavily involved in drugs. One of the brothers runs a Shipping company(i wonder for what).
And still i dont think they are on the same level as Camorra/Ndrangheta bosses for example
