John Evans, 29, had admitted falsely imprisoning Dorothy Miller at his home in Tongham, Surrey, causing her grievous bodily harm and assaulting her. His sister, Joan, 39, admitted one charge of assault. They were jailed for three years and nine months respectively.
Sentencing the pair, Judge Henry Pownall told them that they had treated Mrs Miller, 66, in "quite an appalling way".
Mrs Miller, who weighed 7 stone, was so terrified of John Evans, 28 stone, and Joan, 29 stone, that she was too frightened to escape from their clutches, the court was told.
She was rescued when neighbours called the police after hearing her cries, seeing her bruises and watching her in the garden picking up dog faeces with her bare hands and drenched in water.
David Perry, for the prosecution, told the court that Mrs Miller knew the brother and sister because she had once nursed their mother. They invited her to move in with them last year, intending to use her pounds 63-a- week housing benefit and to make her do all the work.
She was made to wait on them hand and foot and in return received very little food which she had to cook herself and the amount she could drink was rationed, he said.
John Evans frequently lost his temper with Mrs Miller, Mr Perry said. He beat her almost daily, punching her in the face and head and kicking her on the floor. His sister was almost always there during the beatings and occasionally tried half-heartedly to stop them, he said.
He told the court that Mrs Miller was now living in sheltered accommodation, but she still could not sleep properly and was terrified that Evans would find her.
John Rouse, defending John Evans, said his client's congenital obesity and his personality had led to psychiatric problems and he had court convictions.
He had been unable to form any normal adult relationships, and would have difficulty in prison because of his size and an indecency conviction, Mr Rouse said.
Elizabeth Marsh, defending Joan Evans, said that she was virtually housebound and extremely lonely and needed training in "the skills of life".Reuse content