If the two "bedrooms" in the attic meet the requirements to be considered "bedrooms" (ceiling height, egress, etc) you may consider selling as a 4 bedroom. If the finished room(s) addition(s) to the attic were not done with permits, to meet building codes and inspected by the building inspector, and not included in tax records, you should not advertise as a 4 bedroom. You may want to check into having the attic inspected and included in tax records prior to selling. If it is not included in tax records, it would not be included in the livable square footage of the home when a buyers lender orders an appraisal, and may be subject to "cost to cure" to restore to original condition, even more so if the buyer is going FHA. The condition of the septic would also need to pass an inspection.