"Look at them Alula! Aren't they adorable?"

The Duchesses Skyla and Alula with their half-siblings As de Coeur,Demoiselle Enchantée and Mademoiselle Sorceille. Bad End Au: Royalty

So yeah, in this AU/verse Skyla and Alula (more known as "princess Erroria") are the oopsie babies product of Duke Blueblood's many affairs. Skyla was left at Blueblood's house and lived her early years being spoiled and pampered by the canterlot elite. Alula on the other hand was raised in Ponyville in a foster home until it was discovered that she was Blueblood's daughter, since she was a pegasus the elite kind of looked down on her. The horrendous nickname of "Princess Erroria" was given to her by some mean schoolmates in Canterlot, when one day she appeared in a "faux horn" made of amber and her wings tucked in a coat, declaring that she wasn't a pegasus anymore, but one of the foals took the coat off her revealing her wings, making her look like a "weird alicorn". Her big sister Skyla jumped on and scared the bullies. Currently Skyla works as an etiquette teacher in Prance and Alula is a very successful writer.

The relationship with their half-siblings is great, both of them adore them, but are a little bit sour by the fact that Blueblood actually took the time to be in their lifes, when he left both of them at the care of babysitters and nanas. Skyla was (and still is) Demoislle's idol, she ADORES her. Mademoiselle was more close with Alula, because she read her stories of knights and sword fights and that was cool~