What forms of evidence is acceptable when trying to prove that an unfair procedure was followed during retrenchment?

Is a recorded phone call from the Managing Director threatening your job before possible retrenchments being looked at sufficient?

What about an email confirming specific business rules and duties that you were responsible for handed over to different individual before being retrenched?

Is if justifiable to retrench 2 out of 3 individuals carrying out the same job functions due to operational requirements?

What if the 3rd individual not being retrenched only started 6 months after the 2 being retrenched?

What if the company decides to take on 16 employees on a lower salary bracket?

I just need to clearly know how the law looks at these things to know what evidence is acceptable to bring up.