Doubts

According to my understanding, Its written Parliament may make "provisions" wrt elections including preparation of electoraal rolls. That cannot be read to mean parliament itself would prepare.

Parliament has power to make provision relating to any matters related to elections of Parliament and State Legislatures as per the Constitution. Under this power, Parliament has enacted RPA 1950 AND RPA 1951 and has delegated all the authority to the Election Commission of India. So as of now, electoral rolls are prepared by EC of India under provisions of RPA 1950.

Further RPA 1951 prevents convict and undertrials from voting. However, prisoners under Preventative detentions are not forbidden from voting.