Complex sentence: His stepfamily knows of this secret fortune and some go to great lengths to discover its whereabouts, while others pretend to befriend him in order to wrangle Fella's fortune away once it is found.
Split into simpler sentences: His stepfamily knows of this secret fortune and goes to great lengths to discover its whereabouts. The others pretend to befriend him in order to wrangle Fella's fortune away once it is found.