As specified in the data sheet under Pin Configuration, the E-pad is also the V- and must be soldered to PCB. The E-pad could not be connected to GND unless you are using single supply where your V- is also your GND.
Hi aliaykan: The LTC6226 seems like overkill on the bandwidth compared to the LTC1968 and LT1782. Also, it has high bias current which will compromise the accuracy of the LTC1968. For a gain of 2, I would recommend another LT1782.
It is clear that you are correct regarding the second amplifier. The AD8011 was selected by my predecessor for its high BW and still low power consumption. We had issued with the board heating up sensitive components close by.