Ans.How many TRIBES were with Moses in the desert? The answer is 12. Each TRIBE reflected one of the BROTHERS; i.e., sons of Jacob. Since there are 12 Tribes, the prophet will come from one of the brethren; i.e., TRIBES. S/he can't come from all 12 tribes. No where in the Chapter does it refer to Jews.
Moses was not technically a Jew. Moses was a Levite. We later find out that the prophet will be of the Tribe of Judah, seed of Jesse. Isaiah 9. Is Muhammad of the seed of Jesse?
When all the 12 Jewish tribes were in front of Moses. The “correct way of address” would be “from you” and not “From Your Brethren”.
The word “Brethren” itself creates a doubt in the minds of listeners.
And I think that in order to maintain the imminent position of Moses amongst Jews, it would be “More advisable” if the prophet like Moses should be from some one, who is not Jew but very closely related to them.
Whether Moses was “technically” a Jew or not, I leave it to Jews themselves.
Then it would be very easy to accept another “Non Technical Jew” as the Final prophet.