Donald Trump is Barack Obama's successor as the 45th and current President of the United States. But what about Trump and Bill Clinton, for example? Can we say Trump is Clinton's successor too?
The word to describe the relationship between two presidents not immediately before/after one another is fellow presidents (example).
"successor" in the singular will usually refer to the "immediate successor". It might be necessary to specify such immediacy:
- somebody's immediate successor (=the person who has their job or position next) Valentinian's immediate successor, Petronius Maximus, was killed in 455. (Source: https://www.ldoceonline.com/dictionary/successor)
However, in the plural "successors" will of course include the immediate and any subsequent successors.