Might be harder than we think. There is a neutral from the utility to the MDP. We don't know if it was also carried to MDPA. But both of them are 3W, so I don't know where the neutral would be landed. If the neutral is available at the two MDPs, you would have to bring it through the ATSs and to the downstream panels EDP and ECDP (which are also 3W), and from there to the new panels.
But I see a far more significant issue. Gen 1 is called a "Separately Derived System," and Gen 2 is called a "Non-Separately Derived System." Someone please check me on this. I don't believe that can happen (i.e., one of each type) at the same facility. An SDS would require the generator's neutral to be bonded to its case, and would require downstream ATSs to switch the neutral (i.e., 4 pole). The Non-SDS would require the generator's neutral to not be bonded to its case, and would require downstream ATSs not to switch the neutral (i.e. 3 pole). The PDF does not show us the complete wiring downstream of the two generators, and it does not say whether the ATSs are 3-pole or 4-pole. So I can't tell if this system was set up correctly.