Reports identified the fatalities as Edwin Nava, 35, driver of one of the two motorcycles hit by the truck, and Alvin Ebrole, 28, who was riding tandem with him.
Those injured were Joseph Fernandez and his siblings Jonas, 9; Jolly Joy, 7; and Jovi 12; their relative Leo Fernandez; Christian Orleta, Melinda Garcia, John Raymond Chua, and Nelson Rosalinda, who were all riding in a tricycle.
Police said the trailer truck, driven by Ruben Ignacio, 56, was negotiating a downward portion of the Ortigas Extension at the Kaytikling Junction in Barangay Dolores when the accident happened at about 7:15 a.m.
Ignacio said he was supposed to deliver bags of cement to a construction site in nearby Cainta town.