please use the link to the manufacturer internet site. There you get the latest and most reliable informations.
Spike:
This is caused by the "track and hold" capacitor and is quite usual for a SAR ADC.
Thus often a buffer OPAMP is recommended.
Read the datasheet "Track-and-Hold Section"
You don't show what's connected to VIN0 and VIN1. The ADC inputs are usually driven by a low impedance buffer, otherwise charge injection of the sampling switches will be observed.