I keep mentioning two different factions and never explaining them, so here are my ideas for the Refugee elves and the Hearthstone humans.
Indigenious to Hearthstone, they travelled from their continent to Sunholt in the last fifty years, and have been tearing shit up ever since. In-game, they'll be the Romans to the Iceholt's humans Gauls: more technologically advanced, with basic writing, nautical technology and consisting of a hundred different cultures united by a shared nationality. They arrive on the eastern shore of the Forevergreen and quickly begin colonizing and making their way across it, forcing the indigenous populations to assimilate as they travel - either willingly or forcibly.
The Hearth view the elves and trolls as just different types of humans - and in the case of the elves, ones that are unusually primitive, and thus unusually uninteresting. Subsequently, their interests are less in trying to assimilate the elves and more in trying to displace them from the vital resources of wood and ore, no matter the consequences.
The main Hearth settlement would be on the northern shore of the Forevergreen, and would be accessible at the ends of the plains area / around twenty days journey from the holt / center of the Forgotten Grove. Scouting parties puppeted by the admins or by players would be available for all PCs to scene with from the beginning, and one of the first major TPs could be a permanent settlement being created on the western coastline - and the tribes having to decide what, if anything, they're going to do in response.
The refugees as a whole represent the entirety of elves from Sunholt. They're not one tribe - they're the Sunholt diaspora, representative of every elfin attempt (and failure) to colonise the southern continent, who've been forced from their natural environments and their homes in a massive flood north. They're trying to escape the humans, but unfortunately it's not working out too well - and they may not be especially apt to be kind to the indigenious Iceholt residents while they're getting over it.
The Refugees are not a tribe in the sense of any of the canon tribes. Instead, they're a diaspora of various elves and tribes who have managed to survive the human onslaught and now are fleeing to survive. There is no central leadership, and there should be relatively few organised tribes in their mass - while the other tribes repesent communities, the Refugees represent individuals.
There'd be some major groups that the majority of refugees come from. One example would be the Plainsrunners, which would be semi-nomadic elves that live separately in family groups of 1-5 elves, but come together as a whole every year to trade / party / Recognise at an event called the Gathering. No central leadership in this case, save for the heads of each family, and they're linked primarily by a shared language and social norms. Another group would be the semi-canon tribes like Wolfhaven from the RPG book - descendents of Two-Spear that fled south rather than north, and that would allow for non-canon Wolfriders on the MU*. Again, Wolfhaven would likely represent individual holts rather than any overarching tribe, and there'd probably be some blurred lines between what makes one a Plainsrunner rather than part of Wolfhaven.
The (hopefully) non-major group would be the non-tribally associated and non-holt associated elves, which would be defined by the players. This could allow for players to create their 'own' tribes without necessarily needing a tribe behind them. If someone wants to create a 'cat elf', then they could create a refugee from a wolfrider offshoot that, in the Forevergreen, adapted their bond from wolves to cats - and other PCs could follow. Two people might want to make Wavedancers, but one wants them to have flesh-shaped gills and the other wants them to survey the seas on rafts. Under the Refugee idea, both would be possible - and if enough players banded together under one idea, then they could create a tribe separate from the Refugees all together.
This would also allow, if we got any old Two Moons players on the server, them to bring over the basic character concepts they had from the old game - without having to accomodate the entire tribe. If a player wants to play their Underworlder, they can without other PCs being worried about the game going all high fantasy on them.
Certain restrictions would have to apply. My personal feelings are that there shouldn't be any animal-blooded elves except for the Wolfriders and their descendents, but certain genetic predilections should be allowed for. (Wavedancers that self-shaped all the original members and their descendents have gills - fine! Wavedancers that fucked fish and produced fishblooded offspring - not so much.) That's my personal biases, though!