The problem is with the selection policy and the fact that all the players are playing at 50% of capacity,
There needs to be total clean-up of the team starting from the batting line-up. I would start with Janneman Malan as opener and look carefully at Elgar - he is at the stage where he makes one good score and then 7 poor ones, Would retain him for one more series and then replace him if he fouls up again.
Du Plessis needs to be captain - but he is more or less in the same boat as Elgar and that is a bad sign as well. If he keeps failing then it is the end for him as well.
The next guy to be considered is Verreyne - though he is still very young.
De Kock is still the best in the lower batting order. However, he is seemingly disinterested and some work on his approach is necessary,
I would also look at the following potential batsmen:-
Markram, Breetzke, Van Tonder, Bavuma and Smuts. Markram failed badly on the Indian pitches was better on SA pitches and is another player with application problems. Together with Verreyne, Breetzke and Van Tonder are the most promising youngsters coming through,