Inspector Romeo Dumawal, Pandis deputy police chief, said 52-year-old businessman Antonio Jaramillo, husband of Mathays daughter Chiqui, was critically wounded with four gunshot wounds in the abdomen.
Jaramillos colon, bladder and small intestine were damaged but no other vital organs were hit.
He was rushed to the Mendoza Hospital in nearby Sta. Maria town where he is said to be in critical but stable condition.
Jaramillos son "PJ" and a companion, whose identity was not immediately available, were unharmed.
Dumawal said the Jaramillos were on their way to their farm aboard a white Mitsubishi Pajero with license plates WKG-544 when they were waylaid.
Dumawal theorized that a long-standing personal grudge against Jaramillo could have motivated the ambush.
Police found several spent caliber .45 shells at the ambush site.
Two witnesses described the gunmen as mustachioed, wearing black jackets, and about 52" to 54" tall.