Having dealt with half a dozen similar problems over the years, I would say
the simple solution is to use a pva modified mortar to bond Aquapanels to
the inside brickwork.
If the outside is being painted, use a solvent based pliolite masonry paint,
which is genuinely water resistant but still gives a matt finish.
As to walls breathing, lime mortar, and other mud hut technology, I'd say
that nothing stops the passage of air through mortar. Okay, walls have to
breathe, but you need to stop them drinking.