As you have undoubtedly found there are plenty Macdonalds and Sutherlands in Sutherland! The sister Ellen born about 1827 is actually Helen and she was born 7 February 1825 to James Sutherland and Catherine Mackay. Catherine Mackay was also known as Keat and Kate. She and James Sutherland married in Dornoch on 18 June 1813 and had quite a few kids. If you look on the IGI you will see them all including your Andrew. Hope this helps a little.
Christine