I think that by verifing that ADC(3) & ADC(4) are operating correctly when the adjacent input is not connected or is shorted shows that the wiring is correct. In addition, the wiring of ADC(3) & ADC(4) is identical to that of ADC(1), with the exception of the resistor values.
The problem occurs, if for example I have a stable voltage connected to ADC(3) that gives me a reading of, say, 1000. The input to ADC(4) is shorted, giving a value of zero.
The short is then removed from ADC(4), and a stable voltage applied to ADC(4). The previous stable input to ADC(3), that was reading 1000, now either drops to zero, or goes up to 4092.
If ADC(4) is now removed and shorted, ADC(3) returns to it previous stable value.
The scenario is the same when ADC(4) is used, and ADC(3) is shorted.