Much like Klein and Northa, Westar, Soular, and Eas were all created through artificial means.
Lord Moebius planned on invading the other parallel worlds for some time, and planned to create a powerful force of invaders for that purpose- at least before he learned of Infinity, and no longer needed an invasion force. However, before he acquired that knowledge, three prototypes were created- Westar, Soular, and Eas, respectively.
Westar was actually considered initially to be a failed prototype, as there were too many errors in his data. However he was kept alive simply in the event that they needed to learn from him. In the end he was included in the mission to capture Infinity anyways.
Soular and Eas aren't considered failures and were created by Klein, as opposed to Westar, who was created by Northa. Soular and Eas were created by sampling the DNA of Labyrinth's most "genetically superior" individuals. I wouldn't really consider them siblings, though. I wouldn't consider Klein as their father either.
Westar was created by that method- but also by sampling Northa's own DNA so there could be hard argument made for Northa being Westar's mother. That said, she would never acknowledge such a thing because she's Northa after all. She has pretty much nothing but disdain for Westar and considers him a complete failure.
Soular and Eas were both raised in a special facility for their own training, while Westar was sent to a children's home in Labyrinth and was pretty much left to his own devices until the purpose of the three prototypes changed, and he was brought to join Eas and Soular in the training facility.