I am replying for John, with whom I work on the Alexander DNA Project.
From the information you have provided I cannot say with any certainty if we have the DNA of your Alexanders in our Project.
We DO have a large family that migrated from PA to Iredell Co. about the time you describe (names including Allen Ulysses, Gabriel, Rowland).They are closely related to a number of other Alexanders who migrated to other areas of the colonies about the same time.They are the "Confused 2" family at our website alexanderdna.org.
I will be happy to correspond more if you wish. Feel free to write me at firstname.lastname@example.org.