Must the brother who wishes to convert his share of the inherited apartment into a commercial shop leave a passage that allows the remaining heirs access to parts of their private shares and to the undivided communal areas, or does the responsibility for providing this access fall upon the other heirs?

The three brothers should sit down and agree on a solution that achieves benefit and repels harm, because reconciliation is best, and it is more emphasized in cases of dispute between kinsfolk. Otherwise, the matter should be referred to the judiciary. If the brother's disposal of his share would lead to blocking the way for others and preventing them from benefiting from their share, then he is not permitted to do so, for the Prophet, peace and blessings be upon him, said: "There should be no harm nor reciprocating harm."