Elmo was the younger brother of Elu Thingol/Elwe
Singollo and of Olwe.
Elf of Doriath.
He was "beloved of Elwe with whom he remained".
Elmo had a son named Galadhon.
Two of Galadhon's sons were Celeborn and Galathil.
Galathil had a daughter, Nimloth.
Nimloth married Dior Eluchil who was Thingol's heir, and they had a daughter, Elwing.
Tales "The History of Galadriel and Celeborn"
Note: Elmo is also said to be in Histories of Middle-earth: Peoples of Middle-earth, which I unfortunately do not have at this time. Others have said that in that book, Cirdan is related to Olwe and more distantly to Elmo.