Five people including cousins of the Islamic scholar Fethullah Gülen have been detained in Erzurum’s Korucuk village.
Earlier this month, police also detained a nephew of Gülen in İstanbul and his niece in Balıkesir.
Critics have lambasted the government for a massive purge it is carrying out that violates the principle of individual criminal responsibility.
Both the mother and father-in-law of Adil Öksüz, one of the main suspects wanted for his alleged role in an attempted coup, were arrested in August.
In a separate investigation in late July, police also arrested the wife of critical Turkish journalist Bülent Korucu and vowed to hold her hostage until her husband surrenders to police.
Turkish government accuses of Gülen of masterminding the July 15 coup attempt despite, according to many analysts, any credible evidence. Some 43,000 people have been detained so far over alleged links to the cleric.