Gave them inheritance among their brethren - This seems to refer to the history of the daughters of Zelophehad, given Numbers 28:1-8, who appear to have been the first who were allowed an inheritance among their brethren.
And their father gave them inheritance among their brethren - This is mentioned as a proof of his special regard, and is also recorded because it was not common. Among the Hebrews the daughter inherited only in the case where there was no son, Numbers 27:8. The property was divided equally among the sons, with the exception that the oldest received a double portion; see Jahn‘s “Bib. Arch.” section 168. This custom, prevailing still extensively in the East, it seems existed in the time of Job, and it is mentioned as a remarkable circumstance that he made his daughters heirs to his property with their brothers. It would also be rather implied in the passage before us that they were equal heirs.