These two phrases describe the same group of people two different ways. Alternate translation: "the leaders of Israel who are also the heads of their ancestors families" (See: [[rc://en/ta/man/translate/figs-parallelism]])
Here the leaders of the families are referred to as "heads." Alternate translation: "the leaders of their ancestor's families" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The abstract noun "counting" can be stated as a verb. Alternate translation: "had helped Aaron and Moses to count the men" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])