the registering authority is approached on behalf of the prisoner for registering a document which he is otherwise entitled to execute, it shall ordinarily be the duty of the said authority to hold a commission inside the precincts of the correctional home for effecting presentation of the instrument for registration in terms of Section 31 of the said Act...
2) since your brother wants to execute relinquishment deed approach sub registrar office
and sub registrar can go to jail premises to register relinquishment deed
3) Section 31 of the Registration Act entails that under special conditions the Registrar can go to the residence of the person’s house to register sale deeds. The High Court read ‘prison’ as ‘temporary residence’ of prisoner, and held that registration.can be done at jail premises