miminuno:
Slaves can communicate with the master on SPI pins(~10,11,~12,~13)? and expanders to give the SCL and SDA?
Yes. Each slave will use 10,11,12,13 to communicate with the master. The master will use 11,12,13 and one Slave Select pin for each slave.
The slaves are then free to use the I2C interface (A4, A5) for the I/O expanders.