Impossible crossovers
Sasshi created Haruhi when he created the new world.
So, Sasshi always wanted the world to be exciting. However, after preventing his grandfather's death by creating a whole new world where he's not dead and moving everyone around and such, he forgets the whole thing and becomes more mature, losing his innocence and his affinity for all of his childhood things. In the creation of the new world, that part of his consciousness is shunted into the creation of Haruhi as a small child with a proper history in the nearby (about 10 miles away) city of Nishinomiya, which is in the same greater metropolitan area anyway. Since the world was created from whole cloth, it's relatively easy for Haruhi to change. Alternatively, Sasshi is Kyon, and Kyon/Sasshi is the reality warper, NOT Haruhi.
We know that Kyon's name starts with either an S-sound or a T-sound, and it's a common line of speculation that Kyon is the one with control of reality. Sasshi lives in the right area to put himself there. As for the different family make up? Maybe he wanted to have someone that was the near opposite of his older sister, and thus we have Kyon's little sister. Abe is Kamina's father.
They both are gainax characters, they both have blue hair and similar face structure. To continue his studies, he transported to the Gurren Lagann universe and fell in love with Kamina's mother.