I'm going...I'm going down the rabbit hole! Going down the "Krangazoids are Krang's sons" road! Like Willie Wonka's Terror Tunnel I go!
I divided them between three mothers, all from political marriages, and divided how they're related by similar colors and personalities.
Melize is the first mother, a queen in her own right, and offered multiple rulers her territory, provided they defeated her in battle and married her. She has the combat might of ten Spartan women, and if you know anything about Spartan women...you didn't screw around. Krang won a fight with her, by marginally outsmarting her. Their three sons are the most bombastic of the six, and certainly with the biggest presence. One is the most logical of his siblings and the head schemer; another is a muscle-minded powerhouse who frequently butts heads with his brother. The third is vain and narcissistic, and has every intention of staying away from his brothers when they all group together; it gets too wild for his taste.
I haven't quite figured out Reka's origin quite yet, but her sons are twins that hatched from the same egg. In spite of being identical, their personalities are split. One was gloomy and morose, the other, a comic ham.
Agla was the third, and was "given" by her father Gaurav, in an attempt for him to gain more political ground. She was the youngest, perhaps too young for Krang's standards. However, he felt that Gaurav was a jerk even by his standards, and whisked Agla away in hopes that he might be able to strengthen her education. Though technically of marrying age, she had only just reached biological adulthood when Krang married her, to his dismay. Initially, he didn't want to have any children with her until she was older, but caved do to his contract with her father. Agla only had a single child because she was so young, and like her, was shy and anxious. Unfortunately for Krang and Agla, Gaurav keeps sticking his nose in where they don't want it. Krang is especially chagrined by Gaurav's refusal to comprehend his eye for invention, and hates having to repeatedly refute that his machines are the source of his vast power. Krang thinks of him as a "backwards, brutish old man".
They're all left to their own devices. Krang discovered loopholes in his agreements that allowed his wives to have lovers. He likes them well enough, but isn't in love with them. He has a bit of a fan!crush on Melize, if only because of her sheer military might. Not a romantic crush, but a "Holy shit, I love what you did in the Battle of Importantplace! And that thing you did in the Field of Blah! <fanscream>" kind of crush.
Next I might try to figure out how Krang got so powerful, besides multiple political alliances. But in short, I imagine it's because he outsmarted everyone. His species, though broken up in multiple kingdoms, holds a heavy brawn>brain mindset, though it varies from place to place - Agla's being the most muscle minded, Melize in the middle, and Reka practically being his assistant in intention...after Drakus of course.