Who is Donald and Margaret Tupper from Fugitive Pieces and what is their importance?

Donald and Margaret Tupper were Professor Athanasios Roussos's only colleagues in the geography department at the University of Toronto with whom Athos's ward, Jakob Beer remained in contact after his death. Donald lived with his wife Margaret dangerously close to the cliffs of Lake Ontario at Scarborough Bluffs. Erosion eventually forces them to move inland.