Here "be fruitful" is an idiom that means to have many children and descendants. Alternate translation: "they will become very many people and have very many children" (See: [[rc://en/ta/man/translate/figs-idiom]])
This can be stated in active form. Alternate translation: "people to live on you mountains as they did before" (See: [[rc://en/ta/man/translate/figs-activepassive]])
When Yahweh says that people will know that he is Yahweh, he is implying that they will know that he is the one true God who has supreme authority and power. See how you translated this in [Ezekiel 6:7](../06/07.md). Alternate translation: "understand that I am Yahweh, the one true God" or "realize that I, Yahweh, have supreme power and authority" (See: [[rc://en/ta/man/translate/figs-explicit]])