A suspected arsonist is accused of sparking a Bay Area house fire that killed his father, 2-year-old niece and 5-year-old nephew — as the victims’ heartbroken family spoke out about the shocking tragedy.

Sergio Rivera-Vega, 32, was arrested for allegedly lighting the blaze Tuesday night at the home in the 200 block of 15th Street in Richmond, where he lived with other relatives.

When firefighters arrived, they found four victims inside the home, including Rivera-Vega’s 47-year-old father, Jose Rivera, who was pronounced dead at the scene.

Three others — including Rivera-Vega’s 2-year-old niece, Joline, and 5-year-old nephew, Andrew — later died…

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