It is well known that the Church regards the bishops as the successors of the apostles.
For example, the Second Vatican Council taught:
This Sacred Council, following closely in the footsteps of the First Vatican Council, with that Council teaches and declares that Jesus Christ, the eternal Shepherd, established His holy Church, having sent forth the apostles as He Himself had been sent by the Father; and He willed that their successors, namely the bishops, should be shepherds in His Church even to the consummation of the world [Lumen Gentium 18].
Does this mean that the bishops are all really apostles, with a different name? Are they successors in that sense?
No. They are the successors of the apostles in the sense that the apostles were originally the highest office in the Church and, when they passed from the scene, they left the bishops in charge.
The bishops thus succeeded the apostles by becoming the highest leaders in the Church, but not by becoming apostles.
Can we document that?
Yes. There is an appendix to Lumen Gentium that clarifies the matter (printed after the main body of the document at the link). It says:
The parallel between Peter and the rest of the Apostles on the one hand, and between the Supreme Pontiff and the bishops on the other hand, does not imply the transmission of the Apostles’ extraordinary power to their successors; nor does it imply, as is obvious, equality between the head of the College and its members, but only a proportionality between the first relationship (Peter-Apostles) and the second (Pope-bishops) [Preliminary Note of Explanation 1].
So, stating that the bishops are the successors of the apostles “does not imply the transmission of the apostles’ extraordinary power to their successors,” the bishops. They are their successors in a different sense.
Ok. But, there were still some of the Apostles left once Peter had been martyred. What would the relationship of an Apostle such as John been to Linus? Who was the subordinate?