Arduino add two spi slaves that has no slave select pin
Ss or cs pin ISS not mandatory for SPI.

A few solutions.


Power on or off the devices. A group pin can do that.
Cut off mclk.
Have a separate sclk pins for individual chips. You will need to share the serial data pins, ored with some diodes or pull up.
Software SPI.


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I'm sure others will come up with more solutions.