Thinking best way to GFCI all those outlets would be to have a GFCI breaker, BUT; with either of 115 duplex in use there will be unequal currents in the two legs of the GFCI breaker. So it will trip????
Is there such a thing as a standard North American 230 volt GFCI outlet? And if so would it also protect any 115 outlets downstream of it?
Or GFCI the first outlet following the 230 volt so it protects both of the 115 volt ones? The 230 volt outlet then being non GFCI protected. Or blank it off?
Same thing could occur with what here is called a 'split outlet' (can double the capacity and/or allow two heavier appliances, especially kitchens, plugged into both halves of same outlet) whereby the tab between upper and lower halves of a duplex 115 volt outlet is removed and opposite 115 volt legs wired to each half.
BTW; As a separate topic; while we have several GFCI protected outside outlets, if necessary to extend power outside from a non GFCI outlet inside the house we used a GFCI duplex outlet that is of a type that does not provided downstream protection to other outlets and mounted it on end of a substantial extension.
Comments welcome. TIA