By playing around with that site address, I found the family tree for Dr. Dupree. His only male sibling was Elijah, born before 1809. Elijah was the first born, and William J. was the last born.

I'm trying to establish Dr. William Joseph Dupree's family relationship to Capt. William Drury Dupree of Pickens County [6th Miss. Cav., 12th Miss. and Ala. Cav., 6th Ala. Cav., Dupree's Independent Cav.]. The family tree at the site mentioned is not complete enough to establish this. Anyone with info?