I am not convinced that even if they were tenants in common that the brother could 'rent' his own half out separatley from the mother.
He may be able to get something from his mother/sister in consideration of him allowing her/them to occupy his share of the property but that woudl not be 'rent' and eligible for HB
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness. Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery. The blossom is blighted, the leaf is withered, the god of day goes down upon the dreary scene, and—and in short you are for ever floored.
Wilkins Micawber, Ch12 David Copperfield
