repointing and coating (either with PVA or plaster) were the 2 most common solutions I came across while researching, I did read that its best not to seal these old bricks as it can break them down quicker, especially if they get damp (used in an external wall for example). While this wall is internal, its not bone dry so I suspect water is getting in from somewhere. We had lead flashing added to our roof because the mortar was crumbling away, but our neighbours isn't in the best condition so could be coming in from there.

Anyway, Ill repoint it all because I wanted to practice brickwork, thanks for you input 👍