There are two Alexander familes in Iredell Co. One is definitely an offshoot of the Mecklenburg Alexanders. The other one is open to debate, but I believe they are related as well, though it is not yet proven.
Abraham Alexander Sr, chair of the Mecklenburg Convention, had a son, Abraham Alexander Jr. Abram Jr bought the Stirewalt-Rumsey Mill on 4th Creek in Iredell Co. His daughter (Dorcas) Eliza Alexander married (William) Hamilton McClatchy Jr, who lived next door. They are my great great great grandparents.
Hamilton Jr had a sister Mary McClatchey, who married David Alexander (blacksmith). There were two David Alexanders in Iredell at this time, analysis of census data, deeds, and other items show the blacksmith to be Mary's husband. He was the son of Allen U. Alexander, of Elk Shoal Creek (now in Alexander Co, but in Iredell at the time).
Allen U. Alexander's ancestors are unproven. Some believe he is related to the Mecklenberg Alexanders, others think he is from a separate family.
Without more specific information I cannot identify your Betsey and Nancy Alexander -- can you give birth dates and other information? I have five women named Eliza/Elizabeth Alexander in my records, and six women named Nancy Alexander. (Maiden names.)
The only McFarland I have in my records is Margaret Emma MCFARLAND, b. 1839, MO. She married Thomas HAILEY. Their daughter Alice L. HAILEY, b. 21 March 1861, MO, married William Hamilton MCCLATCHY, 6 August 1884 in Falls Co, TX.
This William Hamiltom McClatchy was the son of Albert Alexander McClatchy Sr. AA Sr was a son of (William) Hamilton McClatchy Jr, making him the grandson of his namesake. (There were a number of men with this name, keeping them straight can be difficult.)
I do not have any information on PA families named McFarland; I pick up the search in NC, and have only a small amount of information relating to the Alexanders and McClatcheys in PA.