A search through the 1840 census of Russell Co does not reveal any CARDENs. There are many possible explanations for this, but the simplest explanation is that they weren't in Russell Co in 1840.
The 1850 census does show all three families in Russell Co. Benjamin is family number 242 on page 17. William and Randolph are families #1061 and #1062 respectively on page 76. That William and Randolph are roughly the same age and living next to each other certainly supports the notion that they are brothers. Benjamin is rather far away and is nine years older than William.
William and Sarah are shown with a fifteen year old son named John. This calls into question the statement about them losing a son John when they arrived in Alabama. There is also a son John in the Randolph CARDEN household. If a young John did die, then he would have to be the son of Benjamin CARDEN.
So far, no evidence has been found to even suggest that Benjamin CARDEN is in any way related to William or Randolph CARDEN.
If these three CARDENs were not in Russell Co in 1840, where were they? The 1840 census of Barbour Co AL, which is next to Russell Co, shows a William CARDEN with the enumeration of
I believe this is our William. The two males age 0-5 are John and Matthew. The female 0-5 is Mary. Against this idea is that the 1850 census of William in Russell Co shows a daughter named Elizabeth age 11. I have no further information about her. If she were indeed age 11 on 01 June 1850, then she should show up on the 1840 census as a female age 0-5.
The 1840 census of Meriwether Co GA shows
I think this is a fairly easy call. The male 5-10 is Samuel. The male 0-5 is James. The female 0-5 is Mary. There are no other Randolph CARDENs floating around. Meriwether Co is specifically mentioned in the Russell Co article. This is the guy who shows up in Russell Co AL living next to William.
Benjamin CARDEN is a little harder. There is a Benjamin CARDEN in 1840 Pike Co Georgia
This Benjamin CARDEN is the son of John CARDEN of Jasper Co GA, so we have the Jasper Co connection. Is this the Benjamin that shows up in Russell Co AL? Maybe, maybe not. Benjamin of Pike Co GA doesn't show up anywhere else in 1850. The children of 1850 fit into the slots of 1840, but there are kids in 1840 that disappear by 1850. I think the two Benjamins are the same, but I welcome arguments to the contrary; and I definitely would welcome further evidence one way or another.
I think the key to identifying William and Randolph is the 1840 census for Randolph. He is enumerated in Meriwether Co GA between a David FOLDS and a James CARDEN
Marriage records of Jasper Co GA show that David FOLDS married Nancy CARDEN in 1831. How is Randolph CARDEN related to James CARDEN? James CARDEN is the son of William CARDEN who died in Jasper Co in 1824. From the estate records we know that the only other son of William besides James was William CARDEN Jr who was a minor in 1824 and reached his majority in 1826. This tells us that Randolph is not a (much) younger brother of James, nor is he a nephew. The obvious answer is that Randolph is the son of James. James CARDEN married Elizabeth TILLER in 1807 in Oglethorpe Co GA. Estate records in Oglethorpe Co establish that Elizabeth had a brother named Randolph. I think it is a safe conclusion that Randolph CARDEN is the son of James CARDEN.
To sum up everything; William and Randolph CARDEN of Russell Co AL were sons of James CARDEN and Elizabeth TILLER. They arrived in Russell Co AL after 1840. Benjamin CARDEN of Russell Co AL is NOT their brother, but is a son of John CARDEN who also lived in Jasper Co GA.
Any additonal evidence, for or against, would be greatly appreciated.