You're not imagining things, I really am posting fic! lol
This is the The OC/Brothers & Sisters crossover where Ryan is the biological son of William Walker, making him half brother of the Walker kids. And Sandy told him the Walkers wanted nothing to do with him, but then Ryan found out the opposite is true, and he's getting to know his new siblings, but he's not on good terms with Sandy or Seth at the moment because they're both being stupid jerks...
Last Part: Ryan got arrested for trespassing while trying to help Kaitlin get away from an abusive Frank and a neglectful Julie, and he called Kevin to bail him out, but Justin and Sarah came too. Sandy showed up and revealed the cge fighting meltdown, and Ryan revealed more of his past to the Walkers, who put some of the pieces together and realized just how damaged Ryan is.
( Part Six )