Please read the SARS site link I posted. They say they combine the taxable incomes. IE if the combined jobs earn you R350k per anum, SARS will tax you on the 350k bracket, not on the tax for say, 200k and 150k, seperately. So you will pay a higher tax earning that than your neighbours where the husband and wife team earn 200k and 150k respectively.
Please go read up on the definition of marginal tax rate. That's exactly what I'm saying.