House of Sand and Fog

Abandoned by her husband, recovering drug addict Kathy Nicolo, living alone in a small house near San Francisco Bay Area, ignores eviction notices erroneously sent to her for nonpayment of county taxes. Assuming the misunderstanding was cleared up months ago, she is surprised when Sheriff's Deputy Lester Burdon arrives to forcibly evict her. Telling Kathy that her home is to be auctioned off, Burdon feels sympathy for her, helps her move out and advises her to seek legal assistance to regain her house.
A former Imperial Iranian Army Colonel Massoud Amir Behrani who fled his homeland with his family, now lives in the Bay Area working multiple menial jobs. Living beyond his means, he maintains the faÃ§ade of a respectable businessman so as not to shame his wife Nadereh, son Esmail, and daughter Soraya.
Seeing the auction of Kathy's house in the newspaper, he buys it for a quarter of its actual value, intending to improve and sell the house. Meanwhile, Kathy is evicted from the motel she is staying in. Having nowhere else to go, she spends the night in her car outside her home, the next morning Kathy is angered to see her house being renovated and confronts the workers, injuring her foot. Nadereh and Esmail treat her wound, but her jealousy at seeing how the Behranis have settled in only makes her more determined to get her house back.
Taking Lester's advice, Kathy finds an attorney who assures her that because of the county's mistake, they will return Massoud's money and the house will be restored to her. Massoud, having already spent money on improving the house, is unwilling to accept anything less than the much higher appraised value of the property, which the county refuses to pay. Informed that her only option is to sue the county, Kathy instead tries to convince Massoud to sell back the house for what he paid by telling him she and her brother inherited it from their father. Massoud refuses and angrily forces Kathy back into her car.
Desperate for help, Kathy seeks out Lester and seduces him into abandoning his wife and children and becoming her protector. Using a pseudonym, Lester confronts Massoud and threatens to have him deported if he refuses to sell the house back to the county. Massoud reports this to the police and identifies Lester from a photo, resulting in a reprimand by internal affairs, and gives Kathy a furious warning to back off and leave him and his family alone. Now aware that Lester is in trouble, Kathy calls her brother Frank, but cannot bring herself to admit that she is homeless, and he is unable to help her.
Despondent, Kathy first considers driving to the house and burning it, but after becoming drunk attempts suicide in the driveway with Lester's sidearm instead. Massoud finds her in her car drunkenly unable to discharge the gun, and brings her inside. Kathy again tries to kill herself with pills, but Nadereh saves her by inducing her to vomit. As she and her husband carry Kathy to the bedroom, Lester breaks into the house, retrieves his sidearm, sees Kathy unconscious, and locks the Behranis in their own bathroom, refusing to let them out until Massoud agrees to relinquish the house. Massoud eventually offers to sell the house back to the county for the price he paid and will give Kathy the money in exchange for her putting the house in his name. Lester agrees to take Massoud and Esmail to the county office to finalize the transaction, and Kathy reluctantly goes along with the plan.
Outside the office, Lester begins to manhandle Massoud and Esmail seizes Lester's gun and aims it at him. Massoud grabs hold of Lester and screams for help, drawing the attention of nearby police officers who misinterpret the situation and shoot Esmail. Massoud is arrested but is released after Lester confesses, and is incarcerated.
Massoud rushes to the hospital and while he is there he prays, begging God to save his son and vowing to make whatever changes he needs to in his life. But he finds his son did not survive. Distraught and grief-stricken, Massoud goes home and, believing they have nothing left to live for, kills Nadereh by lacing her tea with pills. He then dons his old military uniform, tapes a plastic dust cover over his head, and asphyxiates himself while clutching his wife's hand. Kathy eventually discovers the couple and frantically attempts to resuscitate Massoud but she is too late. As the bodies of Massoud and Nadereh are taken away by paramedics, a policeman asks Kathy if the house is hers. After a long pause, she quietly replies, "No, it's not my house."

Question: Why did Massoud kill himself and his wife?
Answer: death of a son.