Complex sentence: By 2000, the Russian business environment resulted in the brothers selling all their Russian assets as they focused their business activities mainly in the UK property market, where they have a substantial portfolio of debt-free assets.
Split into simpler sentences: By 2000, the shift in Russia's business environment resulted in the brothers selling all their Russian assets. They focused their business activities mainly in the UK property market, where they have a substantial portfolio of debt-free assets.