Here follows an alternative answer, but only in words.
Dissolving ammonia in water will establish an equilibrium between ammonia and ammonium ions determined by the concentration and the equilibrium constant. The pH of such a solution will be alkaline. Suppose the pH is 10.5.
By the titration with the strong acid HBr, all ammonia should be considered to be transformed to ammonium ions at the equivalence point. Since we have added a strong acid to the ammonia solution, the pH will drop to about 5 - 6.
The interesting part is what you get at the equivalence point.
The equivalence point will be exactly equal to dissolving pure ammonium bromide in water in the same concentration as you have at the equivalence point. What will the outcome be of doing such a thing?
Well, the ammonium ions of ammonium bromide will react with water and equilibrate. Ammonia will be formed in equilibrium with ammonium ions This is similar to what we had at the starting point, when ammonia reacted with water. The big difference is that the pH is not the same. A new equilibrium will be established. At the new (lower) pH the relative amount of ammonia will be much lower than at the starting point, i.e. before the titration was initiated.
So, even if you have transformed all initial ammonia to ammonium ions by the titration, there will be ammonia present at the equivalence point because of the new equilibrium established at the lower pH.