Your main priority is keeping the breathability. The best way to address this is to spot prime the patches where the previous paint cannot be removed with Bonding Primer (please be aware these patches will not be breathable). Then prime the rest of the unpainted area with Silicate Primer. For the second coat apply a mixture of 20% Silicate Primer and 80% Silicate Masonry Paint over the whole area including the areas that have been spot primed. Then finish with a final coat of Silicate Masonry Paint.