Well, from the information that you have provided here, I can find a number of offences in terms of the Sexual Offences Act and you can take this to the police.
Blackmailing in itself is a crime. The fact that he forced your wife to degrade herself sexually, that would constitute a crime. The fact that he send pornographic material of himself without being asked, that is sexual assault. All of those things can be reported to the SAPD and since this whole campaign of violence against women and children is still fresh in their minds, they will probably proceed to investigate and prosecute.
As for civil steps, you would only be able to cite him if you do actually get divorced and there is no guarantees that you will succeed, unfortunately. So, my advice to you is to start with the police.
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