Basis for the generation understanding:
(Exodus 1:6) 6 Joseph eventually died, and also all his brothers and all that generation.
Here we are talking about family relationship, the Insight book has the following explanation:
*** it-1 p. 917 Generation ***
When used with reference to family relationships, a generation can refer to a group of descendants, as sons and daughters or grandsons and granddaughters.—Job 42:16
Job 42:16 shows four generations within a 140 year period.
(Job 42:16) 16 After this Job lived for 140 years, and he saw his children and his grandchildren—four generations.