AN: This isn't necessarily the 'first chapter' but a first look for the base premise of the idea.
AN2: This idea involves Raven having raised Jaune and Cinder (two people we saw in the show had a ludicrously fast learning rate) as she saw potential in them. She's somewhat different in the show and that's because I'm giving another reason for her leaving by acknowledging a discrepancy in the show. I got the math because we know Yang and Ruby's birthdays, we know that Yang is two years ahead of Ruby at Signal, and from what I got online schools tend to have the cut off date being in August for entering a year. Yang's at the very tail end of her school year bracket and Ruby is at the beginning with that metric.
AN3: the year thing was just because I couldn't find an actual named year system for Remnant, so I just used things like 1995 and 1996 from our world.
Family Found and Loyalty Earned
"Taiyang…why are they here?" Ozpin felt his eye wanting to twitch as he looked at not just Glynda, Qrow, and Taiyang in his office but the man's two daughters.
"This is about my mom, I have a right to be here!" the young Miss Xiao-Long snapped, glaring angrily, ignoring her father's rebuking glare. Although with what was about to happen, he couldn't blame his soon to be student for being angry.
"Could you explain exactly what this is all about?" Qrow frowned "All I managed to get was this was about my sister."
"Glynda and I were away from the school for a few days." Ozpin sighed "And during that period we left Peter in charge of testing any new applicants who weren't entering from the prep schools. Two entries passed that exam with flying colors. What got our attention as they listed one Raven Branwen as their mother. I've asked them to come here today to figure out if its just a case of two people with the same name, a prank, or…"
"Or she has other kids." Qrow sighed, rubbing a hand down his face.
"Adopted admittedly, they're Miss Xiao-Long's age, but yes." Ozpin nodded as his scroll alerted him that they were coming up the elevator with one of the faculty members "And here they come now." The door opened to reveal the two teenagers. The first was a tall and broad young man, clearly focused on offense and strength with his fighting style given the dark iron gray armor and the two hammers at his waist. The young woman with him was wearing a catsuit along with several vials along her person.
"Huh, wondered how long it would take for this to happen." The blond boy, Jaune, grunted when he saw who was in the office, leaning against a column along with his sister while the faculty member who'd escorted them quickly left.
"Pardon?" Ozpin raised an eyebrow.
"Mom said you'd probably drag us both up here to interrogate us." Jaune shrugged, I just didn't think you'd do it this fast."
"I told you they would Jaune." The black-haired girl, Cinder, rolled her eyes with a smirk "Meaning I win our little bet." The blond's response was irritable grumbling. The warm sibling like banter was apparently more than Miss Xiao-Long was willing to tolerate.
"You have a lot of explaining to do!" the brawler yelled, eyes blazing blood red and hair aflame.
"No, no we really don't." Jaune shook his head.
"Yes you do!" Yang screamed, not letting Ozpin or the other adults get a word in edge wise "Why?! Why did she leave me?! Why did she choose you?!"
"Oh, he never told you, did he?" Jaune's smirk turned into a cold glare as he looked at Tai, much to the confusion of all but the siblings who'd just entered his office.
"What are you talking about?" Qrow frowned "Raven left because she wanted to. She had problems with Oz and working for him sure but how is that Tai's fault?" as Qrow asked, Ozpin noticed a confused expression with a hint of worry on the man's face.
"So, he never told you he was cheating on mom?" Jaune raised an eyebrow while Cinder scoffed.
"And you never figured it out on your own?" the girl added while the room went dead silent.
"W-what?" Tai's daughters seemed to be the most stunned by the accusations "D-dad wouldn't do that!"
"Wouldn't he?" Jaune pushed off the column, glaring coldly at Taiyang "And you never noticed the signs? Let's look at this shall we? Yang, you were born on July thirty first of the year 1995 while your sister was born October thirty first of the year 1996. That's sixteen months, nine of which she wouldn't have been born yet. That leaves seven months after Yang here was born for Ruby to be conceived. Mom didn't leave the day you were born so you're telling me you see nothing wrong with Mom leaving your father after learning of his cheating, him moving on, entering a new relationship, and getting to the point he'd be ready to have a child with that new person all in under seven months? Grow up."
"She learned he was sleeping around with his partner Summer." Cinder scowled coldly at the name while the Qrow, Tai, and Tai's daughter's all flinched at the vehemence "And Qrow was already too loyal to their little team leader and Ozpin to risk siding with lest Ozpin take efforts to 'keep her around'. So, she left to the only family that hadn't betrayed her, the Clan."
"But that doesn't explain why she'd leave me!" Miss Xiao-Long's fury came back with a vengeance, likely in an attempt to deny what was being said.
"She didn't want to bring you to the clan before she took them over and got some changes pushed through. By the time she did Summer Rose had already moved in, fully convincing you of whatever story she and Taiyang had cooked up." Jaune shrugged "Mom found me and Cinder in…less than ideal situations that she saved us from, took us in. Good for us to given how disturbing I'd guess growing up with the cheating bastard is."
"Disturbing?" Qrow frowned, seeming torn between fury, denial, and confusion.
"The man had his first-born walk around with a hairstyle almost identical to his first estranged wife while he has his youngest dressed in a Lolita version of said wife's outfit." Cinder smirked as Tai's daughters suddenly look remarkably green, not that Ozpin could blame them.
"If that's all, Cinder and I are gonna go back to our hotel." Jaune smirked "So long."
"Hold up." Glynda scowled at them "There's still the matter of you being part of a bandit clan?"
"You mean like how Qrow and Mom were when you first let them in?" Cinder raised an eyebrow.
"Plus, you have no proof of any crimes we've done." Jaune smirked back "Not to mention the necessity the clan is for Mistral with how many Grimm we kill in our wanderings."
"What?" Ozpin had a sinking pit in his stomach.
Jaune seemed to be enjoying this as he answered, "The Clan only takes what it needs when we pass through an area." A statement vague enough to be potentially interpreted as not criminally related so not a confession "And we kill any Grimm we come across. Now, should something happen to the clan, such as us having to relocate should Beacon try to hold me and my sister hostage, then imagine how Mistral would struggle to deal with the sudden loss of manpower roaming and Fighting the Grimm. So long you lot, see you when school starts."
The second that door closed, Qrow snapped and decked a very pale and guilty looking Tai in the face.