Are these pcb layouts good?
Let me start by saying that I have not done a complete review of your design.  Doing that properly would take hours, and I just don't have that kind of time at the moment.  Given that, below are my comments in no particular order.


You need much more capacitance on the power input and the +/-9v
outputs of your converter.  I would recommend something in the range
of 22-100 uF.  What you have there is a switching regulator and you
need some caps to keep it fed, and to smooth out the output ripple. 
I would also increase the size of the caps on the "output" side of
the inductors to at least 10 uF.  22 uF would be better.
The REF5025 needs a 22 uF cap on the output, according to the TI
datasheet.  Additionally, if you intend this to be low noise then the
chip should be located on the same PCB, and ideally right next to,
the chip that needs the 2.5v.
The LP2985, the +5v regulator, needs (you guessed it) more caps.  At
least 10 uF, 22+ uF would be better.
The filtering on your preamp will filter the noise out quite well. 
Unfortunately, it will also filter out your signal.  It has a cutoff
frequency near or below 1 KHz.  You probably want something else.
Here is the frequency response from my own simulations.

You should put your preamps on the same PCB as the ADC's, for lowest
noise. 
Consider removing the 22 ohm + 4.7 nF filter on the output of your
preamps-- but look at the app notes for the ADC and follow their
recommendation for filtering.  Depending on the ADC, this could
increase your total noise.


That's all I have right now.  Basically:  More caps and less PCB's.