A Chevy Chase couple has been ordered by the county to demolish their partially renovated home — or to move it 1.7 feet back from the property line. Marc and Marianne Duffy believe they are victims of a backlash against oversized homes being squeezed into small lots in older neighborhoods. They say they are being punished for a county agency’s mistakes. Neighbors who opposed the construction believe the Duffy’s problems are their own creation. Marc Duffy, an attorney, and Marianne Duffy, a stay-at-home mom and former attorney, served as their own general contractors on the project. ‘‘Three times my husband...