You are right about Joshua Everett and Margaret Buchanan. After being married in western Pennsylvania, they lived in Wellsburg, (W) Virginia, where he was a cooper. You may already know that for many generations the family was involved in glassmaking in several locations, ending up in Columbus working for Federal Glass. I suspect that Joshua made the barrels that were used for packing the glass for shipment back in those early days. I have a copy of his estate sale that includes his cooper's tools.
Margaret Buchanan was probably Joshua's second wife, but I've had difficulty proving that definitively.
Feel free to contact me via email through ancestry.com.
Linda E. Hayden