As with many things in Tolkien, the exact number depends on which drafts you consider to be canon. This answer is mostly in supplement to Wad Cheber's, but with canon sources added. However, the case of Eluréd and Elurin is more nuanced than Ask Middle-earth makes it seem.
But, easy ones first:
Elladan and Elrohir
The canon is covered in my answer to a similar question.
Amrod and Amras
The seven sons of Fëanor were Maidros [> Maedhros] the tall; Maglor a musician and mighty singer, whose voice was heard far over land and sea; Celegorn [> Celegorm] the fair, and Cranthir [> Caranthir} the dark; and Curufin the crafty, who inherited most of his father's skill of hand; and the youngest Damrod and Diriel [> Amrod and Amras], who were twin brothers alike in mood and face.
History of Middle-earth X Morgoth's Ring Part 3: "The Later Quenta Silmarillion" Chapter 1 "The First Phase" V "Of Eldanor and the Princes of the Eldalie"
Eluréd and Elurin
This is something Tolkien changed his mind on, repeatedly.
Initially, the sons of Dior were not twins; in The Genealogies, Tolkien writes:
Elboron son of Dior born 192; Elbereth his brother born 195
History of Middle-earth V The Lost Road and Other Writings Part 3 Appendix: "The Genealogies, The List of Names and the Second 'Silmarillion' Map"
"Elboron" and "Elbereth" would later be replaces with "Elrun" and "Eldun", and eventually "Eluréd" and "Elurin."
Later on, in a plot synopsis written while writing Narn i Chîn Húrin, he changed this:
500 Elrun and Eldun twin sons of Dior are born.
History of Middle-earth XI The War of the Jewels Part 3: "The Wanderings of Húrin and other Writings not Forming Part of the *Quenta Silmarillion" Chapter I: "The Wanderings of Húrin"
However, he changed his mind at least one more time, writing very late in his life:
Dior [Beren and Luthien's] son, it is said, spoke both tongues: his father's, and his mother's, the Sindarin of Doriath. For he said: 'I am the first of the Peredil (Half-elven), but I am also the heir of King Elwe, the Eluchil.' He gave to his elder son the name Eluréd, that is said to have the same significance, but ended in the Beorian word reda 'heir'; to his second son he gave the name Elurin. (the problem of ros)
History of Middle-earth XII The Peoples of Middle-earth Chapter 12: "The Problem of Ros"
Elrond and Elros
Unlike Eluréd and Elurin, Elrond and Elros seem to have been twins for their entire textual history; the last mention of this is in a note added to The Tale of Years:
528 Elros and Elrond twin sons of Eärendil born.
History of Middle-earth XI The War of the Jewels Part 3: "The Wanderings of Húrin and other Writings not Forming Part of the *Quenta Silmarillion" Chapter V: "The Tale of Years"
The year was later changed to 532, but otherwise remains unchanged. This isn't entirely surprising, since Elros was a late addition to the narrative.