Adam Clarke on Exodus 6:20

His father's sister - דדתו dodatho. The true meaning of this word is uncertain. Parkhurst observes that דוד dod signifies an uncle in 1Sam 10:14; Lev 10:4, and frequently elsewhere. It signifies also an uncle's son, a cousin-german: compare Jer 32:8 with Exo 6:12, where the Vulgate renders דדי dodi by patruelis mei, my paternal cousin; and in Amo 6:10, for דודו dodo, the Targum has קריביה karibiah, his near relation. So the Vulgate, propinquus ejus, his relative, and the Septuagint, οἱ οικειοι αυτων, those of their household. The best critics suppose that Jochebed was the cousin-german of Amram, and not his aunt. See Clarke's note on Exo 2:1.

Bare him Aaron and Moses - The Samaritan, Septuagint, Syriac, and one Hebrew MS. add, And Miriam their sister. Some of the best critics suppose these words to have been originally in the Hebrew text.