As an England fan, it looks like you're carrying a few players that aren't good enough. Perhaps it's because there's not a lot else out there. I know Stephen Cook keeps being mentioned, and he should probably come in now, but I can't see him being the ultimate answer.
van Zyl, Bavuma, Vilas, de Kock, Morris and Piedt look nowhere near test standard. Viljeon has got a lot of pace, but if that's his usual line and length, then he's in big trouble at this level. Faf du Plessis is a good player, but much like Ian Bell, he probably needs to be put out of his misery and have a break.