You are right, in so far as what YOU say you should do won't help.
You are extending the procedure given, so you need to do some things to the test tubes given as well.
1. You know which two are sulfates, and you know which two are halides. Let's start by distinguishing which sulfate is which.
What are the differences in reactivity between the NH4+ and the Na+ ions based on the reagents you're given?
You need to remember your analytical tests. Identification of the ammonium cation is done by adding dilute alkali, and testing the vapour above the solution with moist litmus paper (or indicator). Adding alkali affects the reaction; OH- + NH4+ -----> H2O + NH3. Ammonia vapour is alkaline, and will turn the universal indicator blue. Only one of the sulfates will respond to this test, obviously, so you now know which is which.
2. The other two
You have solutions of barium chloride with sodium chloride and potassium bromide.
Silver nitrate reacts with halides, this you know and forms precipitates as you say. So adding silver nitrate to these two will form precipitates of the chloride from the barium, and either a chloride or bromide from the two tubes. You will not be able to tell based on the colours really, the cream will be undetectable, so another test is needed. Silver chloride dissolves in dilute ammonia solution. Silver bromide does not. Add dilute ammonia to these test tubes; the AgCl precipitate will dissolve, the AgBr precipitate will not. Hence, the KBr solution is the one whose precipitate with AgNO3 will not dissolve in dilute ammonia solution.
Happy?