[William Cloud Hicklin]

Tolkien wrote little or nothing about them.

He did name the Seven Houses of the Dwarves: three, the Longbeards (Moria/Khazad-dum) and the Broadbeams and Firebeards (Nogrod and Belegost) were in the West; "The other two places were eastward, at distances as great or greater than that between the Blue Mountains and Gundabad: the arising of the Ironfists and Stiffbeards, and that of the Blacklocks and Stonefoots." That's about it. There is a mention that in the War of the Last Alliance "all races, even birds and beasts" were divided and fought on either side, save the Elves: "but the kindred of Durin of Moria fought for Gil-Galad." This implies, since the survivors of Nogrod and Belegost had been absorbed by Moria, that it was some of the Eastern dwarves who fought for Sauron.

The Elves who refused Orome's summons were the Avari, who (in the late conception) never enter into any of the tales. It is possible, though never said, that Elves of the Journey were lost on the way, but the only breakaways mentioned are those of the Nandor, who quit rather than cross the Misty Mountains (and became the Elves of Mirkwood and Lorien, or the Green-elves of Ossiriand); and those of Elwe's following who missed the boat and stayed in Beleriand: the Sindar. Both these groups were however "Eldar" since they at least began the Great March, and their tongues (in the late conception) descended from Common Eldarin.