Hi I've simple differential configuration amplifier with ref powered from 1/2VCC VCC is 3.3V. Differential signal is output from AMC1200. When I tried to power it up I have nothing on output.
I apologize for misunderstanding your configuration. It is clearer with your schematic. Yes, I think it would be better to tie the resistors of the high pass filter to mid-supply. The problem looks like it could be the input common-mode going into the inputs of the AD8236, it does not go fully to ground. The AD8226 can sense slightly below ground, and that is probably why the setup is working.
You can also use this design tool to ensure that you operate within the limits of the in amp:
Instrumentation Amplifier Diamond Plot Tool | Analog Devices