The problem is in the schematic you linked. The issues are twofold: The V_BIAS input is set to a midpoint DC value, equal to half the supply voltage, and secondly there is no negative supply rail for the instrumentation amps.
The VOCM pin is the Output Common Mode Voltage, meaning the average DC output voltage you wish to see on the two outputs, when the (differential) input voltage is zero. You use this pin to adjust the output DC offset to whatever you want/need, including zero.
However, to be able to adjust the output common mode voltage to zero, you almost certainly need a negative supply rail to the inst-amps. Just having ground as negative probably wont work here. Haven't looked in the datasheets, as I cannot read exactly which devices you are using.
As a first test, try removing R6, 1K to AVDD1, and check the output voltage. This should give zero volt on VOCM, and thus zero average out. But you won't be able to drive anything near zero/ground. Also, for this to work, the devices need to be able to work down to the negative supply rail.
Also, using two 1K resistors and a single 0.1 uF capacitor is not going to cut it for a low noise reference voltage, if this is for a critical application. Analog Devices have an app note about this somewhere on their site.