Here "my house" represents the nation of Israel. Being faithful in God's house represents being faithful in leading Israel. AT: "Moses leads my people faithfully" or "Moses is the one whom I trust to lead my people Israel" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Yahweh asks this question to rebuke Miriam and Aaron. It can be translated as a statement. AT: "You should be afraid to speak against my servant, against Moses." (See: [[rc://en/ta/man/translate/figs-rquestion]])
The phrase "against Moses" clarifies that he is the "servant" of whom Yahweh speaks. AT: "against my servant, Moses" (See: [[rc://en/ta/man/translate/figs-parallelism]])