twee·dle·dum and twee·dle·dee 
(twēd′l-dŭm ən twēd′l-dē)
(twēd′l-dŭm ən twēd′l-dē)n.
Two people or two groups resembling each other so closely that they are practically indistinguishable.
[After Tweedledum and Tweedledee, names of two proverbial rival fiddlers, of imitative origin.]