Here "all of Israel" means those people mentioned afterwards. They represent all of Israel. Alternate translation: "spoke to the commanders ... heads of the father's house"
Possible meanings are 1) these numbers represent the exact amount of soldiers that these commanders led. Alternate translation: "the commanders of 1,000 soldiers and the commanders of 100 soldiers" or 2) the words translated as "thousands" and "hundreds" do not represent exact numbers, but are the names of larger and smaller military divisions. Alternate translation: "the commanders of large military divisions and the commanders of smaller military divisions" (See: [[rc://en/ta/man/translate/translate-numbers]])
Here "the heads of the fathers' houses" further describe the princes. Alternate translation: "to every prince in all Israel, that is, the heads of the fathers' houses"
Here "heads" is a metaphor for the most important part. And "houses" represents families. Alternate translation: "the leaders of the families in Israel" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-metonymy]])