The victims received what was initially described as life-threatening burns and stab wounds after Abedi threw boiling oil on them and attacked them with "homemade weapons", according to the prison officers' union.
The attack, which is being investigated by the police, occurred on a high-security unit at Frankland Prison in County Durham in northeastern England on Saturday.
One of the prison officers, a woman, has been discharged from the hospital. The other two are being treated for serious injuries.
Hashem Abedi is the brother of suicide bomber Salman Abedi, who carried out the attack at an Ariana Grande concert in Manchester in 2017, killing 22 people.
Abedi helped his brother prepare the bomb and was sentenced to life imprisonment for murder, attempted murder, and preparing a terrorist attack. The brothers are linked to the terrorist group IS.
In 2022, he was involved, along with two others, in another attack on two prison officers.
