I am not sure why you have chosen the SPI_SpiSetSlaveSelectPolarity API. This API allows you to choose slave select line polarity, means whether you want your slave select to be active low or active high.
As per my understanding, in your case you will need to change the SPI clock modes since the two slaves are working on different clock phase and polarity. Please correct me if I am wrong.
You can try using an Unconfigured SCB and configure it for SPI operation with CPHA = 1 and CPOL = 0 clock mode while using Slave (0) and reconfigure the SCB to SPI with CPHA = 0 and CPOL = 0 when there is an interrupt from Slave (1).
Hope this helps. Unfortunately there is no sample project for this exact operation.