We have a 1920's hunting/fishing cabin and the brick chimney was made with a sandy mortar which is failing now. The chimney buckles in the middle with the upper half slightly leaning over the cabin roof. I've been told it has to go for safety's sake from one chimney expert and another said he could save it. I'm inclined to agree with the first guy because he explained that the mortar will just keep on breaking down over the years to come and there's no proper footing for the weight of it. Can we demolish this safely ourselves and how - 1 story about 15-20 ft tall probably. Also I'd love to save the huge fossilized stone mantel and surround inside, but can we buy a gas direct vent fireplace and just slip it in the existing hole? Thanks for any advice - my adult sons and husband have moderate skill levels.