The Votans are not a single species, but a collection of seven different alien species who evolved on a number of planets in the Votanis star system. The different races banded together to flee their star system when it was destroyed in a stellar collision, and ultimately arrived at Earth.
The Votanis star system was destroyed in a stellar collision 5,000 years ago, but the millions of Votans who fled in ark-ships made the long interstellar journey in hypersleep, thus many of the older Votan characters were born in their home star system and lived under their old social structures before they had to evacuate.
For example, older Castithans such as Datak and Stahma grew up in the caste-based society on their old homeworld, but younger Castithans born on Earth grew up after the Castithan social hierarchy broke down when they lived as refugees. Thus there is something of a generational divide between those Castithans who immigrated to Earth, who possess an older value set, and their second generation children raised on Earth (such as Datak and Stahma's son Alak).
The Votanis star system was located in the Perseus Arm of the Milky Way galaxy. It was actually a binary star system, composed of the stars Vysu and Solus. Vysu was orbited by two habitable planets, Daribo and Irath, each of which had one habitable moon. Solus was orbited by one habitable planet, Casti. The Indogenes and Castithans evolved on Daribo, and the Castithans later colonized Casti (hence its name).
The Irathient, Sensoth, and Liberata evolved on Irath. Together they were known as the "three worlds" and the "twin suns", though soon before the evacuation fleet departed, the Gulanee were discovered on the neighboring gas giant Gula, and the Volge on the planet Omec.
The Votanis Collective is the unified government of the Votans, formed to escape their home star system, though since the Pale Wars many Votans have (like humans) factionalized and broken off to carve out their own small fiefdoms. The Castithans, Indogenes, and Irathients were the most politically powerful races in their home star system, thus they made up a disproportionately large number of the survivors in the evacuation. Because they were politically weaker, relatively few of the Sensoth, Liberata, or Gulanee were present in the evacuation fleet.
The Votanis Collective is officially an alliance of five races, excluding the Gulanee and the Volge. So few Gulanee survived to arrive on Earth that they are not considered a separate faction, but are simply spread out among the other races of the Collective. The artificial Volge are hated by all other Votan races, and are the enemies of humans and other aliens alike.
The Castithans and Irathients loathe each other, as their societies are based on idealistically opposite values of hierarchical order and rugged, chaotic independence. In contrast, the other four races besides the Castithans get along together quite well. The Irathients, Liberata, and Sensoth all evolved on the same planet where they peacefully co-existed for generations, while the rational Indogenes are also quite tolerant and try to get along with all of the other races.
Most of the other Votan races, while not outright hating them like the Irathients do, see the Castithan as arrogantly trying to assume control over the other races. The Indogenes have a complicated relationship with them, because the Indogenes are very tolerant, but at the same time, the fact that they and the Castithans evolved on the same planet has led to each bickering over which of their two races is superior. Meanwhile, the labor-minded Liberata are just content to serve anyone, even the Castithans.
When the Votans arrived at Earth, the United Nations granted them a limited settlement area in Brazil, created by clear-cutting massive areas of the Amazon rainforest. The Votans named this new colony "Sulos" (after one of the stars in their home system). Over the next decade, the Votans were granted three further colonies: "Irath" in Peru, "Indo" in Guatemala, and "Omec" in the Oaxaca region of Mexico.
Humans were upset that any territory was being given to the Votans, while the aliens were upset that they were essentially being ghettoized in glorified refugee camps. During the Pale Wars, these colonies became the core territories of the Votanis Collective, and even 15 years after the war during the events of the TV series, Sulos in Brazil remains the capital of Votan territories on Earth.
At least some Votan species are capable of procreating with humans, to create hybrid offspring. It has been stated so far in Season 1 that Castithan-Human and Irathient-Human hybrids exist. They are however extremely rare, as such an exotic pregnancy is dangerous to both the mother and the child.
It is unknown if humans can interbreed with some of the more exotic Votan races, i.e. the Liberata who breathe nitrogen instead of oxygen. It has not been mentioned if there are hybrids between the different Votan species themselves, given their closer evolutionary relationship relative to humans.
Linguist David J. Peterson designed the Castithan and Irathient languages for Season 1 of the TV series, as well as basic sketches for the Indogene and Liberata languages. As of Season 1, Peterson has not begun work on languages for the Sensoth, Gulanee, or Volge.