The only Collinwood/Old House sets used in the '91 series were Collinwood's foyer/great hall/drawing room and Barnabas' bedroom. Everything else was shot inside Greystone. That would include all the other bedrooms in both houses, Collinwood's dining room, breakfast room, kitchen, second floor corridor, servant's wing and closed off wing/library, and the Old House's foyer, drawing room, and even the basement. (The basement also doubled as the sheriff's office.)