For example, I turn #2 encoder to a position, then turn # 6 to a position, then #3 to a position without disturb together. Is that possible ?
Any combination is possible. The thing to look out for is codes that are too close to each other to reliably read and decode.
Note that any encoders in position #3 essentially shorts out the resistor across AB so it should be considered 0 ohm when calculating the R1 and R2 values. Also, the short would be across all the resistors in between multiple encoders that are switched to AB (pos#3).
An alternative is to just measure the codes (ADC count) you get for all combinations you're interested in and create a look-up table of values.
EDIT: Will be away from my PC for a few weeks ... good luck with your project!