Purpose of capacitors and extra resistors in the feedback of the inverting op amp?
It is a fairly standard ADC driver topology.

Modern ADCs often have switched capacitor architectures that need a fairly large cap local to the input to provide the very fast current pulses that the things draw while performing the conversion, 10nF is a bit larger then you usually see, but not orders of magnitude so.

Now, opamps do not do well directly driving capacitive loads, as it can very easily cause a stability problem, but often you really want good accurate control of the ADC input voltage, so what is a guy to do?

The first thing you do is place a resistor between the opamp and the cap, a few tens of ohms is typical, which isolates the capacitive load from the opamp output, but hurts accuracy, as the feedback is now taken from the wrong side of that resistor (But at least the thing no longer honks)... 
If you move the feedback tap to the load cap side of the resistor then the effective output impedance goes down, but now you have the stability problem back again.
However, the phase shift due to the load is frequency dependent so by placing a cap directly around the opamp then you can ensure that both the gain rolls off with a corner at roughly 1k2 * 820pf, and that at high frequency the feedback phase angle is dominated by the 820pF cap and not the phase lag due to the 10n cap. 

At low frequency the gain as seen at ADC3 is -1.2/7.5 with good dc accuracy, there is a -3dB breakpoint at w = Rfb * Cfb, which serves to both limit the bandwidth at the converter and reduce the stability damaging phase lag from the 10nF cap at high frequency.