Remove render and repair crack in stone wall

hi Marie Sorry to hear about all the problems you have had with damp and neighbours etc. It sounds like you have penetrating damp problems even though the gutter has been repaired. The render should come off easy with a hammer and bolster and you can even hire small tools which would do the same job but much easier. Once the old render is off then the stone or brick behind it may need re-pointing and sealing with a Thompsons masonry sealer or similar which keeps out water. The render is then reaplied in 2 coats sand cement and possibly lime and then painted with a decent masonry paint i.e. Sandtex or similar. With regards to inside make sure the room is well ventilated and remove any damaged plaster where salts are visible. You can also buy a solution for removing the mould and a mould resistant paint should help as well. Remember though if you are working at heights outside make sure its properly scaffolded for health and safety reasons. If the crack appears to be further down the building inside and out then there could be something more sinister in terms of a structural problem i.e foundations or deflection over a window or door which needs more investigation? Hope this helps