What are all the ways Elrond and Galadriel are related?

Question

In answering this question, I discovered three relationships between Galadriel and Elrond:

1. Galadriel was first cousin of Elrond’s great-grandfather (Turgon, King of Gondolin). Thus, they are first cousins thrice removed.

2. Elrond was the great-great-grandson of Fingolfin, brother of Finarfin, Galadriel's father. Thus, they are first cousins thrice removed through another line.

3. Galadriel’s grandfather (Olwë of Alqualondë) and Elrond’s great-great-grandfather (King Elwë Thingol of Doriath) were brothers. Thus, they are second cousins twice removed.

4. Elrond was married to Galadriel’s daughter, Celebrían (which also makes Galadriel the grandmother of Arwen, obviously). Thus, Galadriel is Elrond's mother-in-law.

This is already a pretty complicated web of relationships, but Tolkien's genealogies are so detailed that I'm not convinced I've found every connection.

Are there any other relationships between Elrond and Galadriel?

Answer 1

There is one more, but it's stretching canonicity, and also what you might call a "relationship."

In some writings, Galadriel's husband Celeborn was the grandson of Elmo, brother to Elu Thingol and Olwë (Galadriel's grandfather¹):

Galadriel, coming to Middle-earth as one of the leaders of the second host of the Noldor, met Celeborn in Doriath, and was later wedded to him; he was the grandson of Thingol's brother Elmo - a shadowy figure about whom nothing is told save that he was the younger brother of Elwë (Thingol) and Olwë, and was "beloved of Elwë with whom he remained." (Elmo's son was named Galadhon, and his sons were Celeborn and Galathil; Galathil was the father of Nimloth, who wedded Dior Thingol's Heir and was the mother of Elwing.

^{Unfinished Tales Part 2: "The Second Age" Chapter IV: "The History of Galadriel and Celeborn"}

The passage I quoted above also includes the main thrust of this new relationship, which is that Celeborn's brother Galathil was the grandfather of Elwing, Elrond's mother.

Therefore, Galadriel is Elrond's first cousin, thrice removed, by marriage.

The reason I say this is questionably canon is that Tolkien's last writings on the subject (and some of his last writings ever) establish Celeborn's heritage differently: in them, Celeborn is the grandson of Olwë (thus making him and Galadriel first cousins, which would be...odd²), and we know nothing of Galathil. In this later version, there's no indication that Celeborn and Elwing are related.

I found another one

You're going to love this.

So, Galadriel is Lúthien's first cousin, once removed, which makes her Beren's first cousin, once removed by marriage.

Beren's uncle, Bregolas, is the great-grandfather of Tuor, father of Eärendil and grandfather of Elrond.

So Beren and Elrond are first cousins, four times removed.

So, Galadriel is the first cousin, once removed by marriage of Elrond's first cousin, four times removed.

What do you even call that?

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¹ Which would make Galadriel and Celeborn second cousins, fact fans

² Tolkien had established in earlier writings that Elves marrying first cousins was a cultural taboo; Maeglin, for example, is considered a deviant for desiring Idril, the daughter of his uncle:

[H]e loved the beauty of Idril and desired her, without hope. The Eldar wedded not with kin so near, nor ever before had any desired to do so. [...] [I]t seemed to her a thing strange and crooked in him, as indeed the Eldar ever since have deemed it: an evil fruit of the Kinslaying, whereby the shadow of the curse of Mandos fell upon the last hope of the Noldor.

^{The Silmarillion III Quenta Silmarillion Chapter 16: "Of Maeglin"}

And he writes in "Laws and Customs" that the practice was rather uncommon, except among long-sundered branches of the family (which probably wouldn't apply in Celeborn and Galadriel's case, since both were of Aman):

'[F]irst cousins', as we should say, might marry, but seldom did so, or desired to do so, unless one of the parents of each were far-sundered in kin.

^{History of Middle-earth X Morgoth's Ring Part 3: "The Later Quenta Silmarillion" Chapter 2: "The Second Phase" Laws and Customs Among the Eldar}