This is probably the number one reason you are here. Through your own research you have found a list that said your family surname belongs to the Clan Farquharson. Your question now is probably how. That unfortuantly is a much tougher question, but not one without a few answers.
The word "sept" has been given to a family that is associated with a particular clan. A family might join a clan for military protection, food, money, extending family relationships, or the possibility to improve prestige. The families who would join a clan were generally in the same geographic area. Due to the reasons why a family would attach itself to a clan are often the reason why some families may find themselves on different clan listings, or more sadly not on any listing at all. In cases like this you will have two options either pick the clan you decide to join, or pour your heart and soul into geneology and you may be able to find the exact actions of your family. From personal experience this is an extremely tedious approach that may or may not give you any definite answers.
I have to take a second to address the Lord Lyon. On his website there is to be found the following statement "There is no official list of recognised septs. This is a matter for each chief to determine. But where a particular sept has traditionally been associated with a particular clan it would not be appropriate for that name to be treated by another clan chief as one of its septs." This statement in my opinion is the single most complicating arguement ever made to any one trying to define themselves to a Clan. There are plenty of records to show the diffusion of names over areas and the commonality of certain names. Are we to beleive that the MacDonalds of Braemar were really connected to Clan Donald or even Clan Ranald? For those of you with unique surnames to the Clan Farquharson lands I offer you this statement, go with your instinct or most well informed guess as to the clan affiliation. Or go with what you want, remember one important aspect of clan affiliation was allegiance.
I beleive a brief note on the Mac/Mc controversy is needed. The common surname prefix Mac means "son of" in the Gaelic language. Contrary to popular opinion the spellings of Mac, Mc, or M' has the same meaning . There is no truth in the belief that those with the Mc are from Ireland and Mac from Scotland. In the course of history there have been changes in which form of Mac is in fashion.
The Farquharsons like most clans had more than one branch. The Clan was often less centralized than we have been lead to beleive. Every day activites of the clansmen and women were the duty of the local leader. Amoung the Farquharson branches were Balmoral and Monaltrie.
The following is a list of surnames associated with the Clan Farquharson. The links will provide you with some detail as to the association with the Clan.