There is nothing wrong with the choices you have made for the amplifiers. The instrumentation amp is not noisy, the amps have plenty of gain, and your bandwidth is modest, so I see no problem with the amp choices.
Have you confirmed that the amplifiers are working by substituting an alternate input signal? If so, can you adjust your alternate source down to a very low level to confirm the gain of your amplifiers?
If the system works with an alternate source of signal, then you must suspect your electrodes or the physiology.