Peter and Paul were saints only in the New Testament meaning of the word. Canonization by the church does not make anyone a saint except in the eyes of man. In the New Testament the Greek word hagios...
St. Regina remained steadfast in her Christian faith even in the face of torture and death. When the proconsul Olybrius wanted to marry the humble shepherdess and demanded that she abandon her...
They are, like Saints Cosmas and Damien, often grouped together, but they are not "co-saints" just grouped together because of their importance as early disciples.