Amplify difference between two photodiodes
For my application, the only relevant data is the difference in
luminosity between these photodiodes.

If both photodiodes are the same, wire them antiparallel to a single TIA. Wiring them antiparallel means that the only current feeding the TIA will be the difference current. Now, the problem of noise is halved. Use a balanced transmission system like this: -

Replace the sensor on the left with a single ended op-amp driver and use balanced cable such as shielded twisted pair. Ground the shield at the receiver end. Clearly you need to use a differential receiver amplifier too. Schematic from here.
The two resistors marked with a blue X represent equal impedance resistors so that a balanced impedance drive to the cable is facilitated and any interference (red lightning symbol) has to affect both inner transmission wires equally. That is what is meant by &quot;balanced&quot; in this context. Of course, with the spare components from the unneeded TIA you can drive the line differentially and increase SNR by another 6 dB.