A pair is simply two of something, so whether or not they are related is irrelevant:
A “pair” - one male, one female - is no different than a “pair” - two males - is no different than a “pair” - two females - is no different than a “pair” - one ball python, one corn snake
As far as inbreeding is concerned, there are lots of opinions on the matter. These posts in a rather lengthy discussion elsewhere on the boards sum up my personal feelings