A far more honorable race than their compatriots, the Kallusians are nevertheless a desperate species. In the comics, this race was caught up in the war between two other alien empires. They were finally forced to flee their homeworld, and for a time lived as a nomadic race without a home of their own. Ultimately, the Kallusians found their way to Earth, and established an underground base at the North Pole. There they remained for years, hiding from the warring aliens who began to hunt them out.
The Kallusians only ever appeared in one comic, 1965's Avengers #14. That saw the aliens discovered, and briefly fought by, the Avengers; when the Kallusians learned their presence had been discovered by their enemies, they left Earth to do battle in the stars. The final page featured a cameo from the Watcher, who revealed that the war would have destroyed the entire planet had not the Kallusians honored their word.
Presumably the Kallusians in the Confederacy aren't based at the North Pole; they seem fairly disinterested in Earth. It seems more likely that the race has been reinvented as a space-based nomadic people, although given their allies, the MCU version may not be quite so honorable.
The final named race are the Astrans, and they're one of the better-known members of the Confederacy. In the comics, the Astrans are a race who are at a similar stage of technological development to Earth - with one notable exception. These aliens possess the power of "ferro-kinesis," and are able to manipulate metal in a similar way to the X-Men's Magneto. The Astrans typically use these powers for artistic purposes, but have also succeeded in creating powerful star-drives for interplanetary transport.
Probably the most well-known Astran is a Hulk villain named Molyb, who calls himself the Metal Master. An Astran criminal, the Metal Master sought to use his powers for conquest. He traveled to Earth, and used his powers to demonstrate his superiority; missiles were swept aside, tanks were melted away; every weapon humanity possessed was dismissed with a scornful wave of the Metal Master's hand. He's been a minor recurring villain ever since.
Depending on their MCU power-levels and abilities, the Astrans could well be the most dangerous members of the Confederacy. Their ability to manipulate metal on an atomic level would make them a terrifying potential threat.
One Final Unknown Race
Finally, and most curiously, Agents of S.H.I.E.L.D. stressed that there are six members of the Confederacy - and deliberately avoided naming the sixth race. There's likely a reason for that; either the sixth race will somehow be relevant to season 5's plot, or Marvel Television have plans to use the Confederacy beyond Agents of S.H.I.E.L.D. season 5. It's even possible this could be a rogue Skrull House, just as House Kasius has separate itself from the rest of the Kree. That would allow Marvel to link the Skrulls into their TV shows, while again not worrying too much if Marvel Television and Marvel Studios portrayed the race in a different way in next year's Captain Marvel.
The Confederacy are easily Marvel Television's greatest contribution to the cosmic side of the MCU to date. This alliance has lasted for over a thousand years, and built up its own dangerous traditions and rituals. Should Agents of S.H.I.E.L.D. be renewed for a sixth season, Marvel may well choose to develop them as a terrifying threat for Coulson and his team. Even if they don't, though, the fact remains that this sixth race could easily be integrated into any of Marvel's TV shows.
Agents of SHIELD season 5 continues with “The Force of Gravity” May 11 on ABC.