3 The imperfect tense here should have the nuance of instruction or injunction: “you are to speak.” The subject is singular (Moses) and made emphatic by the presence of the personal pronoun “you.”
4 The phrase translated “everything I command you” is a noun clause serving as the direct object of the verb “speak.” The verb in the clause (אֲצַוֶּךָ, ’atsavvekha) is the Piel imperfect. It could be classified as a future: “everything that I will command you.” A nuance of progressive imperfect also fits well: “everything that I am commanding you.” The distinct emphasis is important. Aaron will speak to the people and Pharaoh what Moses tells him, and Moses will speak to Aaron what God commands him. The use of “command” keeps everything in perspective for Moses’ position.
5 The form is וְשִׁלַּח (véshillakh), a Piel perfect with vav (ו) consecutive. Following the imperfects of injunction or instruction, this verb continues the sequence. It could be taken as equal to an imperfect expressing future (“and he will release”) or subordinate to express purpose (“to release” = “in order that he may release”).

In other versions

You shall speak all that I command you, and your brother Aaron shall tell Pharaoh to let the people of Israel go out of his land.

You are to say everything I command you, and your brother Aaron is to tell Pharaoh to let the Israelites go out of his country.

You must say whatever I command you; then Aaron your brother must declare it to Pharaoh so that he will let the Israelites go from his land.

Tell Aaron everything I command you, and Aaron must command Pharaoh to let the people of Israel leave his country.

You will speak all that I will command you, and Aaron your brother will speak to Pharaoh, and he will release the Israelites from his land.

Thou shalt speak all that I command thee: and Aaron thy brother shall speak unto Pharaoh, that he send the children of Israel out of his land.

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