Veela are quite possibly one of the most interesting subjects within the Harry Potter Franchise. Facts about them, however, are few and far between, at least in the books themselves. I've not read any supplementary works, so I don't know what else Rowling has come up with, but this hasn't stopped fan fiction authors from coming up with their own information concerning Veela.
What we know about them is that they appear human and are able to cast magic with a wand like normal Witches and Wizards, they have an allure that they can use to ensnare at least men turning them lust-addled, they have an avian form that they take when angry, and they can conjure fire. Fan fiction authors expand on this to describe the Veela life cycle and other such things that aren't explained by the books.
It seems fan fiction is pretty evenly divided between the camp that allows for half and quarter Veela and the camp that says that you are either Veela or you are not. I believe I'm in the latter camp, and explain it thus: Veela genetics are dominant such that any child of a Veela and a human male can have the dominant Veela genetics, though only females will be Veela. Male children with the genetics have a small chance to pass them on to their children, though; there are no male Veela.
Another very popular fanon is the Veela life cycle, where a Veela child will grow to a certain point, then remain at that size looking still like a little girl, then after a certain number of years they go through a rapid maturation into their adult form. I can get behind this, going as far as saying that at age 8 or 9 they stop growing for about 7 years, then at 15-16 they go through a maturity that gives them the body of an adult. While the mind and emotions continue to mature in the adolescent Veela, the body remains childlike for so many years.
Why am I going over this, though? Simple, I had an idea after (re-)reading Emerald Coven recently and thought of a story where Gabrielle is the same age as Harry. Only using my explanation requires me to go even further. Veela are sexual beings, and the reason that they stop growing is to allow them to begin sexual experimentation without having to worry about having a body mature enough to get pregnant. Thus I can get Harry and Gabrielle together while they are still small children and they can begin a life of sexual debauchery before even attending school!
Setting is when they are both 8 years old and something happens to drive Harry away from the Dursleys and Gabrielle finds herself separated from her family. They meet and become close to one another, and find a way to live on their own. Gabrielle explains about herself and they start experimenting from a young age. Really, this is just my excuse to write/read a story with preteen sex in it. Thanks to my version of Veela maturation, I don't have to worry about them possibly having children before/during Hogwarts, at least until their fifth/sixth year when Gabrielle finally grows up.
Not sure if I want to include anyone else in their relationship the way Emerald Coven does. If I do, it might be early, and it might wind up getting some people pregnant in first/second year. Not that that's all that different from many of my other stories...
Anyways, not much detail, just general concepts and whatnot. I'll have to revisit this sometime...
Okay, so continuing my thought from my last post, I've come to borrow an idea from the story Rose Lily Potter -- Metamorphmagus-Who-Lived and make Harry a Metamorph, though the ability lies dormant until he's 8. Further, I'm tweaking Lily Evans to have the dominant Veela genes that survived countless generations since her only magical ancestor, and having James pass on the Metamorph genes, meaning Harry is in a unique situation such that if he assumes a female form, he is a Veela.
So, concept is that Vernon brutally beats Harry in downtown London and leaves him, and Gabrielle finds him due to his whimpering while her family is in town there. He's crying out softly for someone to help him, and in that moment her Veela magic reaches out to him and bonds to him rather tightly. Shortly after that, the last Potter House Elf responds to Harry's cry for help and transports Harry and Gabrielle to the Potter Manor, where Harry's trauma causes him to assume female form (his thoughts being that he wanted nothing more to do with men if they were all like his uncle, thus triggering the metamorph talent and transforming him into his female, and therefor Veela, form).
When the kids awaken, Gabrielle introduces herself and is momentarily confused when Harry identifies himself as such, then realizes that the boy she had found must have been Harry before becoming this Veela girl in front of her. She take's the new girl into the adjacent bathroom to show her what she now looks like, and she's startled to find a rather cute looking girl staring back in the mirror. Gabrielle explains that she must be a Metamorph and further a Veela. It's at this point that Harry takes on a new name: Primrose, after a flower that she was fond of in her aunt's garden.
Shortly after this, the last Potter House Elf appears and introduces himself as Alfred, and the newly christened Primrose starts to learn a bit about her heritage. Gabrielle also explains about Veela and what it means to be Veela and about their situation binding the two of them together. Primrose is overwhelmed, but somehow manages to deal with it.
Gabrielle's parents and sister are at first worried about her being missing, but Appoline, her mother, is able to sense what's going on with her daughter, including that she's far from London now and has activated her Veela bond with another. Due to the nature of this bond, she knows her daughter is in good hands, and the family is left to wait for her to come back to them when the time is right.
Primrose and Gabrielle spend the next three years learning, both about magic and the world, and especially about themselves. Gabrielle works to get Primrose used to her new body, then they begin to experiment to figure out what they like and dislike sexually. Within a year, Primrose has a grasp on her Metamorph talent and begins to experiment with her own gender, and Gabrielle gets the chance to experiment with sex with a boy. Three weeks before they would turn 11, they both get letters from Hogwarts inviting them to go there for their magical education.
Now it should be stated that Primrose never again takes on a fully male form; instead, she simply uses her talents to "grow out" the male genitalia that she needs to use them. Let it also be said that she leaves her female genitalia alone, meaning they are still there. In fact, under normal circumstances, she prefers to keep both sets at all times, just in case the two of them suddenly get in the mood. This doesn't mean that Primrose wore boy clothing all the time; she actually highly enjoys wearing dresses and skirts and other girly things. The two girls do, however, tend to go naked when alone in the house more often than not.
As for Hogwarts... I'm not sure. The two will be sorted Gryffindor, but other than that I don't know. I do know that the Veela bond doesn't count as a marriage; I also know that Veela, being sexual beings, will desire relations with many different people. What I'm getting at is that the two of them together will prefer to bed others and generally form a harem around each other, and that their first preference is girls, though if they find a boy worthy of them they won't say no.
Other than that, I don't really have anything else. This is an interesting concept that I kind of want to run with, but I feel as though I don't have the right background knowledge to do it justice... Well, I guess I'll just have to see about it...
Now I had another thing or two to add to this that hit me a few minutes ago. Not gonna cut it because forget about that. Anyways, I just had to clarify about Veela; as I mentioned before, they are sexual beings, but also sensual beings, and tactile sensory is something they crave. Further, while a Veela can and will settle down with a single person, some prefer not to do that and will willingly have relations with many different people in their life, sometimes at the same time. This is the type of Veela both Primrose and Gabrielle are and they will more or less collect people to have casual sex with over their Hogwarts career.
Also, although neither Primrose nor Gabrielle are capable of getting pregnant until they mature, either by having Primrose fuck Gabrielle with her male parts or Primrose and Gabrielle selecting a male lover, Primrose is still capable of impregnating other girls, as they will likely find out very early on in their Hogwarts career. A few girls will become permanent parts of their harem, if only due to their providing new family for the pair. I'm only looking at three that early, though... Hermione, Susan, and Daphne, though how I pull it off, I don't know.
And really that's it. They will seek out people for casual contact and sex, but will also always be together due to their bond. I really don't have any more to add.