I'm agreed with you - Brandes was a quality bowler and another for whom Test Cricket came just a tad too late.
Mbangwa was miserly accurate but not much more than that. Throw in that he competes with Chris Martin for the title of worst test batsman of the last 25 years and his inclusion in this team is difficult to build a case for IMO.
Olonga was very similar to Devon Malcolm - lethal on his day, just that day didn't come along that often.
Depending on the balance of the side, my bowlers would come from:-
Automatic picks - Streak, Brandes
Then any two from - Brain, Blignaut, P Strang, Price
Batsmen - G Flower, Whittall, Campbell, Goodwin, Houghton, A Flower
All-rounder - Johnson