The announcement of the arrests comes as Israel faced mounting pressure to bring the attackers to justice, with a UN Middle East envoy on Wednesday expressing concern over the "slow progress" in the probe.
"We have confirmed that a number of suspects have been arrested in connection with the incident that took place in Duma," Israeli police spokesman Micky Rosenfeld told AFP.
Far-right Jewish activist jailed for setting fire to school in Jerusalem
The Shin Bet domestic security agency said arrests had been made in recent days of young men "suspected of belonging to a Jewish terror organisation and carrying out terror attacks."
It said in a statement that those detained were being questioned over the July 31 firebombing in the West Bank village of Duma.
Further details of the investigation remained under an Israeli gag order, often used to keep details secret of sensitive investigations.
The Dawabsha couple's four-year-old son is the sole survivor from the immediate family of the firebombing.
Palestinian teen killed by Israel army fire
The attack led to widespread condemnation globally as well as by Israelis and Palestinians, but no one has been charged for the killings.
Palestinians have often highlighted the lack of progress in the case as among the causes for a wave of violence that began on October 1.
The violence has included Palestinian knife, gun and car-ramming attacks.
Palestinian toddler burned to death in 'settler' arson attack
Since the start of October, 104 people have been killed on the Palestinian side, including an Arab Israeli, while 17 Israelis, an American and an Eritrean have also died.
Many of the Palestinians killed have been attackers, while others have been shot dead by Israeli security forces during clashes.
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