So you are drawing 52A per phase so it will sum to more than 39A.
Remembering that you have 2x2x13A socket outlets per phase & you are now drawing 13A per outlet, that is 26A per pair, thus the circuit is non compliant, however, you would hope that the circuit protective device would operate, to protect the conductors.
However, at 26A per phase how long would the MCB take to trip, if you were to only connect a single lamp to each twin socket outlet, and would the 2.5 be rated at this for a single phase, in its installed configuration, you would hope it was, and would there be no instances where it could be possible for the N to be overloaded, possibly not in a perfectly balanced loading scenario.
However, you cannot guarantee that this is all that will be connected.
I'm not going to do the maths at this time of night, sorry, I can see where you are coming from and it is possible for the N, not to be overloaded as the circuits could be perfectly balanced. though I doubt it.
Also, I'm now getting very tired and I'm getting to the end of the computer repair I'm doing tonight so it's time for bed as I'm up @ 06:00 in the morning for work.
This will have to continue the next time I am free to debate things.
However, I'm still maintain that the N CAN be overloaded.