The 102-year-old was shot dead in his sleep, with the Islamic State of Iraq and the Levant (ISIL) also killing his son, his grandson, his great-granddaughter and her mother, said the Syrian Observatory for Human Rights.
All the victims were Alawites, members of the same offshoot of Shiite Islam as Syria's President Bashar al-Assad.
Rooted in Al-Qaeda in Iraq, ISIL is the most extremist group fighting in Syria's war.
Initially welcomed by rebels seeking Assad's overthrow, their systematic abuses and quest for hegemony turned the rest of the opposition against them.
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"Some members of the family were burned alive, others killed in their sleep," it added.
Elsewhere, the loyalist air force launched fresh strikes against rebel areas of Aleppo, dropping more, highly destructive barrel bombs, said the Observatory.
Several people were injured in Sunday's attack, and a house was burnt down.
The regime's air offensive on Aleppo's rebel areas has killed some 2,000 people so far this year, and caused thousands of families to flee the city.
Rights groups have blasted the regime's use of barrel bombs as indiscriminate and unlawful.
More than 162,000 people have been killed in Syria's war, and nearly half the population forced to flee their homes.