Who are we?

[Panzram]

A and B had the same first initial, same middle name, and same nickname.
A and B were rookies the same season, both played for pennant winners in their second season, and hit the same number of HRs in their third season.

[Panzram]

Season 1 2 and 3 are the same year for both players, which means same number of homers in the same season (19xx) which was the third in each one's career.