The answer is that the Alexander Sutherland of Earnside was childless, and so left his estate to his brother James, Fiar of Forse.
I have compiled a database of Sutherlands in Jamaica prior to 1835, and may be able to answer your question if you can provide me with more information. It can be very difficult to make links where people have emigrated, unless there is documentary evidence, such as may be found in wills and deeds, etc.
I have in the database a Robert Sutherland who was baptised on 1 Jan 1844 at St. John's Chapel, Highgate, St Catherine, Jamaica. His parents were William Sutherland and Mary Mitchell. His father was deceased at the time of the baptism. Its likely that Mary was of mixed race and that the couple were unmarried. I have no information about William's ancestry. Its possible his will may have survived in the Jamaica Registrar's office, but you would probably need to go there in person to find out, and arranging copies is very expensive.
I do hope this helps.