The two 18-year-old twins who reportedly have sympathies towards Daesh (ISIL) stabbed their mother to death, and later stabbed their father and younger brother before fleeing the scene according to the New Arab news website citing Saudi Watani news agency.
The suspects were arrested close to dawn in Riyadh's al-Dilam neighborhood after crashing their getaway car.
No official statement has been released regarding the motivation of the attack.
However, some Saudi news outlets reported that the brutal attack took place after the parents regularly criticized Daesh and described the group as a terrorist organization.
Meanwhile, Saudi social media users argued that the twins believed their parents were apostates for opposing Daesh.
They shared details of the gruesome incident and expressed their horror that the suspects could commit such violence against their parents, especially during the holy month of Ramadan.
In September, two Daesh sympathizers lured their cousin - a member of the Saudi armed forces - to the desert and shot him dead on the first day of Eid al-Adha, while recording the entire incident.