Yes Khron, I agree... originally, schematic had a dual unit OpAmp... but this design requires a very low quiescent current OpAmp.
I found the OPA145 that uses just 0.475mA per unit, but I could not find the dual version of it. So I had to stick with the single unit version.
To save space, I placed one OPA on the top, and the other at the bottom of the PCB.
I also considered OPA1692, but it's very tiny, may be for a next version.
If you have more options on low current Opas, that could work, plz let me know!
Regards!
HL