Is Twilight appropriate for a 12-year-old?

No. The relationship modelling is horrific, and children are especially vulnerable to false messages on this front.

Don’t teach them that stalking is romantic. Just don’t.

Sure, it’s a good story. But let’s not. Jondo Singing by Julio Romero de Torres. Public domain.

Can you fly an American flag in the UK in your own private property there? What is the UK’s government stance on that? And if yes, do you also have to fly the UK flag or the American flag can fly solo?

Edward and Bella’s relationship starts because Edward stalks Bella. He watches her in her sleep and he followers her around; him following her is revealed when he jumps out to save her, the implication being that it’s good he stalked her. We’re supposed to see this behavior as him loving her, caring about her, and being willing and able to protect her.

But, and this is key, stalkers will also act to protect themselves from their beloved if their beloved falters by acting in less-than-perfect ways.

You can keep it in your books for adults. Adults know things that seem sexy in books can be horrific in real life. But kids learn how to live their lives from the fantasies they read.

Out-of-Body Experiences Could Be Coping Mechanisms Instead of Pathology, New Research Suggests - The Debrief

Which is how many real-life stalkers see themselves. They’re so in love, they can’t help themselves. If anything happened to their beloved, they’d give up anything, take any kind of beating to protect them.

Any genuine interaction risks this, as the stalker is in love with their idea of the person, not the actual person. Behavioral or personality traits, even interests that diverge from that super compelling idea of the person may create revulsion or hatred, up to and including violence, in people who are obsessed with someone.

Rejecting the stalker is even more perilous. This is the harshest possible challenge to their romantic obsession, and they will respond by trying to prove themselves—that is, by intensifying their stalking—or by immediately devaluing the beloved and lashing out, often violently.

What kind of person makes you think "how come there are people like that"?

It’s dangerous no matter how you slice it, life-threateningly dangerous, and encouraging young people to see behavior this toxic as romantic and a sign of love is socioculturally poisonous. We risk people’s lives by teaching them these things.