Vigdis is the first to reach the fairy ring, since, well, obviously she is. She immediately becomes aware of the people gathered there, and then spins around and sees that her half-siblings are frozen, and then spins around again.

" - what the fuck??"

"They'll be here eventually. Here, you can sense time as it really passes, without being slowed down to match the world around you. Almost all humans are slow all the time."

"Who the fuck are you? If you don't mind my asking."

"You can call me Rána; your aunt does. You should not tell me your name; I know who you are, and if I knew it I could never let you go."

"Well that's - good of you to say, I guess," she says, with a pointed look at Catherine. "What are you."

"I am a fairy."

"Oh. Well that's just - all right, fine, s'not weirder than me I guess. Who's that," she says, gesturing at Ingolfr. 

"My youngest son, he's aged about a year and a half since you saw him last. - we should probably cut her off at some point, Rána, I can't see how much any given answer is worth, but she doesn't specialize in poetry and I think she'd better be able to go home if she wants to."

He nods. "You don't want to ask too many questions," he tells her, "because fairies can keep people if you're indebted to us, and answering questions creates debt. We don't want to hurt you. We're planning to show you and Catherine's children around and tell you some things that you need to know about the human king and after that you can make up your mind what to do."

"Arright. This is super weird, just to let you guys know? But I'm gonna go along with it."

She will figure out whether Catherine has been unwillingly kidnapped by fairies and has summoned her to rescue her, like, in a bit, when potential abductor fairy guy isn't, like, right there, probably.

"Wanna see the house we made?"

"...sure. Yeah. OK."

Unless Vigdis is being obvious about her suspicions he will come along to show off the house.

Nope! Vigdis has not been obvious about her suspicions about things since she was, like, seven.

She thinks the house is super cool. Living in a tiny treehouse in the forest seems pretty great, if you're into ditching society.

Some people are.

Probably good when they know how to build awesome tiny treehouses, then. 

At some point she's able to get Catherine alone and confirm that she is not supposed to rescue anybody, at which point she goes back to waiting for Sigrun and Tyr to arrive in the fairy ring.

     Sigrun is the next to come through. She looks around in bewilderment, and then - "Mom?"

"Yes. Hello."

     Sigrun does not ask more questions, she just sort of stares warily at the mostly invisible person.

The mostly invisible person smiles at her. "Do you want to hear a story? A useful story that will explain what's going on, I mean, your mother knows more epic stories than I do and it doesn't really seem like the time for one anyway."

"Yes. I would like that."

"Once upon a time - yesterday - there was a human king who let his human concubine out of her cage for once, and she went walking in the forest with her babies, and she wandered off the trail and met a fairy. Some people will tell you that you should not meet fairies in the forest, for they are strange and terrible and will carry you off to their fairie courts and you'll never be seen again; but this woman knew that humans do that, too, for it had been done to her, and she spoke to the fairy, and he was charmed by her, and he carried her off to his court and she sang poems for them for a very long time, because fairies do not count time the way that humans do. But she had left some of her children behind in the human world, and she missed them, and she dreamed of telling them someday that there was more to the world than they could see, and bits of it that her human king would never conquer, and so she asked her fairy to return with her to Akershus, so that she could see her children again and tell them this, and so they returned, and built a house in the trees, and sent for her children, and now one of them has arrived.

That's my story."

"Mom."

"It's nice here, darling. If you stay a while we can explain more."

Sigrun looks a little bit disgusted and leaves the fairy ring, then spins around to see if they've disappeared again.

Nope.

She walks over to her brother, who's still slow, and attempts to pull him away from the circle.