British Dictionary definitions for tweedledum and tweedledee
Tweedledum and Tweedledee
any two persons or things that differ only slightly from each other; two of a kind
C19: from the proverbial names of Handel and the musician Buononcini, who were supported by rival factions though it was thought by some that there was nothing to choose between them. The names were popularized by Lewis Carroll's use of them in Through the Looking Glass (1872)
Two matters, persons, or groups that are very much alike, as in Bob says he's not voting in this election because the candidates are tweedledum and tweedledee. This term was invented by John Byrom, who in 1725 made fun of two quarreling composers, Handel and Bononcini, and said there was little difference between their music, since one went “tweedledum” and the other “tweedledee.” The term gained further currency when Lewis Carroll used it for two fat little men in Through the Looking-Glass (1872). For a synonym, see six of one, half dozen of the other.