Is there any reason why there is such variance in these lists?
In Genesis (46:21) lists ten sons.
And the sons of Benjamin were Belah, and Becher, and Ashbel, Gera, and Naaman, Ehi, and Rosh, Muppim, and Huppim, and Ard.
Numbers (26:38-40) lists five. Two that are sons of Benjamin in Genesis 46 (Ard and Naaman) are grandsons in this list.
The sons of Benjamin after their families: of Bela, the family of the Belaites; of Ashbel, the family of the Ashbelites; of Ahiram, the family of the Ahiramites; Of Shupham, the family of the Shuphamites; of Hupham, the family of the Huphamites. And the sons of Bela were Ard and Naaman: of Ard, the family of the Ardites; and of Naaman, the family of the Naamites.
There are two lists in 1 Chronicles in successive chapters. Chapter 7 (v. 6) clearly states that Benjamin had only three sons.
The sons of Benjamin: Bela, and Becher, and Jediael, three.
1 Chronicles 8 (v. 1-2) lists five sons
Now Benjamin begat Bela his firstborn, Ashbel the second, and Aharah the third, Nohah the fourth, and Rapha the fifth.
There are a total of seventeen names in the four lists. Only one is common to all four lists: Bela. Ashebel is in three of the lists and Becher and Huppim/Hupham are each in two. Each of the other names occurs in only one of the lists.