Siblings of the Firstborn?

[Taniquetil]

Entmoot,
I finished reading the Sil a while ago, and when I was considering the genealogies of important elves I came across an interesting conundrum.

1. It is stated that Elwe and Olwe were brothers, and other legendarium suggests that they might have had another brother, Elmo, grandfather of Celeborn.

2. That Indis was the niece of Ingwe, implying that he had a sibling.

Yet nowhere have I found any reference to their parents, and surly Tolkien would have at least mentioned the parents of the Kings of Elves if they had them, thus we mist assume that they were firstborn. This idea is encouraged by the fact that Elwe says to the dwarves that "his life began at Cuivienen, long before the fathers of dwarves awoke."

Might this mean that they were found in the same "groups" (by Enel and Imin respectivly)?

Possible Implications: we would have to do away with the theory that Ingwe, Finwe and Elwe were in fact Imin, Tata, and Enel renamed. Up till now I considered this the most likely scenario, after all, who wants to walk around with names that mean one, two, and three, for the rest of their life?
But Imin, Tata, and Enel awoke only with one another and their wives,they had no "groupmates" that could later be called their siblings.

Or maybe Tolkien explained this somewhere and I missed it.
What say you?