Questions about the LPF of input signal chain of LTC2378-20

Dear Analog Engineer Zone, 

While I was looking at LTC2378-20 ADC, I have a question regarding the RC network as shown in the attachment, which is on P10 of the datasheet. 

-- How did you define LPF1 resistor and capacitor value and how did you define the corner frequency of the LPF1, which was used to avoid distortion and noise. 

--  For LPF2, I understand that the 10Ohm and 3300pF are used to provide sufficient settling and get rid of the disturbance of the sampling process, droops or spikes. But what is the purpose of the 6800pF capacitor? How did you pick this value?