When replacing old windows with new PVCu double glazing, make sure the contractor knows what he is doing. These windows were installed without a lintel and the weight of the concrete ceiling bearing down on the plastic frame has caused these stress cracks.
If you repoint old brickwork with sand and cement mortar, it traps moisture in the bricks. The mortar joints are there to allow water to evaporate through them rather than through the bricks. If the moisture is trapped it will then find its way out through the bricks and with frost action, spall the face of the bricks.
These joints should be repointed with a lime based mortar to allow the wall to breathe.