This phrase refers to other priests who would serve in the temple under the leadership of Joshua. Alternate translation: "the other priests who live with you" (See: [[rc://en/ta/man/jit/figs-explicit]])
Here the word "sign" refers to something that communicates a special meaning to those who see it. Yahweh speaks of the priests serving in the temple as being this sign that shows that Yahweh will bring his servant.
The word "Branch" refers to a messianic figure that would serve as king over Yahweh's people. Yahweh speaks of this person as if he were a branch that grows out from a tree. Since the word "Branch" is a title, it should be translated with an equivalent word in your language. (See: [[rc://en/ta/man/jit/figs-metaphor]])