Is the Imam's prayer invalid if a worshiper precedes him in some actions or positions?

The majority of scholars hold that the prayer of a congregant becomes invalid if he precedes his Imam. The kind of precedence that invalidates the prayer is when his heel is ahead of the Imam's heel. Assuming that your father certainly preceded you in the row, his prayer is valid according to the Maliki school of thought, and it is permissible to follow this opinion.