Shared bias voltage for quad op-amp
The input signal is present on the node at the right of R3, so R3 must be duplicated for each channel (otherwise you would be joining all the inputs together!). R1, R2 and C2 can be common to all channels. 

There are two possible issues with using a common voltage divider - bias current, and crosstalk.  

OP295 op-amps have a maximum bias current of 20nA each, so in the worst case you could have 80nA flowing in or out of the voltage divider. The DC impedance at this point is 50k (100k in parallel with 100k) so the maximum voltage change that might be caused by bias currents is 50k*80nA = 4mV, which is probably not significant in your application.  

Without C2, signals could leak from one channel to another through R3 (greatly attenuated perhaps, but still might be audible). However C2 should shunt virtually all of this crosstalk to ground.    

The only thing I would be concerned about is the 1.8V supply voltage. The OP295 is only rated down to 3V.