The property was built with Chimney breasts which passed through the rooms above into the loft and emerged as chimney stacks above the roof. The chimneys would be supported off the natural foundations.
The chimneys are a structural part of the house and should not be altered without professional advice, building regulation approval and party wall notices agreements and awards.
The flues are brick built and would have lime mortar. This lime mortar may have decayed and allow combustion gasses to permeate through the flues.