Complex sentence: Granite Island and the lighthouse were purchased by Scott and Martine Holman in 1999 from the U.S. Coast Guard and underwent a three year restoration process at large expense, and which has inured to the public good.
Split into simpler sentences: Granite Island and the lighthouse were purchased by Scott and Martine Holman in 1999 from the U.S. Coast Guard. The facilities underwent a three year restoration process at large expense, and which has inured to the public good.