The 32MHz crystal is necessary for the radio to operate and stay on Channel. You can choose to use the built in Load Caps or supply your own externally. The values will depend on the CL value of the crystal you are using. Please see the datasheet for crystal parameters.
The softdevice also needs a 32Khz clock. For the least power consumption the external 32Khz crystal is recommended.
Please follow the suggested layout and schematics found in the reference material.
