Parents: Starwood. n.b., PRG does not offer 1.5x everything; EveryDay Preferred does, but only in statement cycles with 30 or more transactions. Regardless, Starwood points are much more flexible than Amex's own points.
Chase United MileagePlus Club ($450/year) offers 1.5x UA miles on everything and Club lounge membership, which may be useful if your parents fly United.
Brother: Chase Freedom.