Hello Daniel,
From wonderful Madrid.
Let me try to be helpful but not too negative.
Your English is first class, by the way.
Let us assume that the half of your family that lives in South Africa can give you board and lodging and that through them you can become a South African citizen.
You are sixteen now and so to finish your education may take two years and another two or three years to get your pilot licences. So the question you have to asks is what might be the employment situation in South Africa airline environment for white citizens. You may say that okay, you will fly charter, but it is the recruiting at the airline level in SA that creates the jopbs through the industry.
In five years time, my private opinion is that SA will be a dead ducky for young male white kids in the line of work you are talking about. The government will just sponsor more and more black kids for the flying posts until enough of them can pass. It is like the bloody Russians coming over the hill in the Stalingrad retreat. Too many of them to kill.
For the rest of your questions that fall in with the specifics, I think you will find that there are all the answers contained within Pprune and the SA CAA website where you will find the requirements of PPL, CPL and ATPL set out. As for your remaining school years, unless you can afford private education, why go the state school route in a country which has the temptation, not always so well resisted, to reduce all the pupils in the class to the level of the dimmest?