Philip Spence, 32, battered the trio from the United Arab Emirates in London's posh Cumberland Hotel in Marble Arch on April 6, Southwark Crown Court was told.
Though Spence has admitted to have attacked the sisters but he denied attempted murder.
One of the victims was hit with such force that her skull split open and she was left with just 5 per cent of brain function.
She survived the attack but despite undergoing emergency neurosurgery she can no longer speak and even lost one eye.
Her sisters Khulood, 36, and Fatima, 31, were also left with life threatening injuries and are still undergoing treatment.
The sisters were attacked when they were holidaying in London.
Spence, from Harlesden in north-west London, was also found guilty of conspiracy to commit aggravated burglary, as was Thomas Efremi, 57, from Islington.
Judge Anthony Leonard told Spence he could face life imprisonment for the attacks.
Spence attacked Khulood as she shared a bed with her two young daughters and then turned his hammer on her sister Fatima leaving both of them unconscious, the court heard.
The fourth sister Sheika Al-Mheiri described the jury how she returned to the hotel to find her sisters injured on the floor with "blood everywhere".
Spence fled from the scene with a suitcase containing iPads, gold jewellery and mobile phones.
He dumped the claw hammer just outside the four-star hotel.
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