sorry went to bed!,, If its TT then the RCDs ar e required, but not all of them I would be looking at trying to remove the 3 phase RCD and fit a main switch then fit rcbo's to final circuits that are fed from the 3 phase board, and an MCB to feed the other RCD protected board..hopefully there aint many ways on the 3 phase board. at least this spreads the loads and any faults will trip the approprate RCD.
okay I've changed a few things around today ... I've taken out the Rcd below board . I've notices as well it seems to trip when it gets a surge of current ie printer or hand dryer. The 3phase braker is an old mem one so could be a problem changing that