Elimination approach:
Instead of recalling the title directly, rule out the distractors by role and period. Dr. Yashwant Sinha and Mr. Arun Jaitley both served as Finance Minister well after 1991 and are associated with later fiscal policy, not the original liberalisation drive, so they can be set aside. Dr. Manmohan Singh, as Finance Minister in 1991, executed the reform package on the ground and is often called its "chief architect", but the honorific "Father of Indian Economic Reforms" is conventionally reserved for the head of government who took the political risk of authorising them.
Sh. P.V. Narasimha Rao, as Prime Minister during the 1991 balance-of-payments crisis, gave the political backing that allowed liberalisation, deregulation and opening to foreign investment to go through - which is why he, not his Finance Minister, carries this title.