We don't know that Raven and Qrow Branwen's mother's name isn't Magpie. We also don't know what their father's name is so I call this fair speculation and not outright disobediance to cannon.
The Meeting of Magpie and Bronze:
She flew over mountains and glen. She flew over humans and all of their setlements. She flew far from home and close to the sky. She saw the world as a place of adventures to be wrapped up in. She was Magpie Glas the Omen.
One day, as she looked down on the black swarms on a baren landscape she saw a flash of silver. She loved all that glimmered even for the stars though they were always beyond her reach. She alighted upon the ground behind a nearby boulder. Feathers to clothes, beak to lips, and talons to feet.
Once her transformation was complete she strode towards the human. He was sheathing his enourmous sword when he turned toward her. The sword was appropriatly sized to the decaying bodies, but not the man. He was some what tall and slightly stocky, but he wasn't the giant needed for the shining blade.
His hand flew to it all the same.
"Who are you?" He asked, implying danger in every movement of his body.
"I know the hermit wizard that lives in the mountains. I know the four sisters who circle the globe that carry his power. I also know the violets that are in a garden they take turns keeping.
I've seen the settlements of humans scattered across the land. I've seen the Grimm that exist to destroy them. I've also seen their demon ruler.
You are none of these. So aren't I supposed to be the one who asks that oh-so-tedious and rarely-ever-answered-truly question?" Magpie the Omen sang back in sing-song.
The man's mouth formed a twisted grin. It was not as bitter as a grimmace, but it was also not as heartwarming as a simle. It was an expression of hunger-lust.
"You say it is tedious, but what is it that is called out in the darkness? 'Are you there?' So asking who you are better let's me know know that you are there," he answered.
Magpie paused. It was an idea that she had yet to consider. That to know who one is helps discern if they are there.
"I... am Magpie, the bird who can take on human form. I live longer than most and have only seen humans as dabs of light on a dark background. You are the closest human I've ever been around. Now I am really curious as to who you are, stranger."
Magpie closed the gap between them and peered into his eyes. They fascinated her, much like the rest of him. The human man stared at her impropriety in perplexity for a moment. Then he gave a more genuine smile. His blade flashed out and sliced a tiny Nevermore on her right side.
"My name is Bronze Smith. I work as a hunter of Grimm. I'm not sure if you really are a bird yet, but I want to talk to and be around you long enough to find out."
"So you fell in love with him Gramma Magpie?"
"Goodness graciuos, Ruby! No. He convinced me that he wasn't an idiot so I became his companion. After that I slept with him. That's how Raven and Qrow came into the grand scheme of things. He ended up dying on the job so I ended up sending them to combat schools to train. Couldn't be birds forever those two. Had to fall in love with freaking humans."
"So Raven was in love with my dad. She just doesn't love me."
"Screw her! I can understand her leaving your fool of a father, but I'll be dammed if I don't chew her out for leaving you there should she ever come back! There's sex without love in this world, Yang, but she defies and denies the word mother. You are my granddaughter without being her daughter. You understand? I claim you as mine no matter what. It is our chosen bonds and not just blood that makes you that my golden star. You have your Gramma's love."
"I love you too Gramma. You said that they both fell in love. Who did Uncle Qrow fall in love with?"
"Humans."
"Gramma, we all know he's had multipul partners."
"Humans as in humanity as a whole, Yang. Even if he was a bird through and through, his love of humans would mean that he'd find any way to interact with them. He wants to fight Grimm and protect humanity. You two especially."
"Are you sure he didn't fall in love with anybody?"
"He's slept with many people, but you've seen the photo he carries around. Tear stained and with a cup mark over the person he treasured and lost. He carries it with him always. My son named himself your uncle, Ruby, because of her. I'd rather you call him father instead of that no account fool Taiyang. That would have been a match I'd approved of. Silver like Bronze." The old woman mutter the last part under her breath.
"Bronze isn't silver Gramma!"
"Next you'll be telling me gold isn't white! You're such silly girls. My gold and silver stars."
Yes, I know. Bronze Smith and Magpie D'Omen. Such creativity. It creates their last names though, so please forgive me. I just wanted Ruby and Yang to say Gramma Magpie. That's the entire purpose of this. Please be laughing your asses of on the other side of the screen. Glas means blue in Welsh, the origin of the name Branwen. It's not a misspelling. Hunger-lust just means intense curiosity.