It moves enough to be slightly worrying if I didn't know that was typical! It looks like it's moving such that it might crash reasonably soon. 

"It's... not going to crash. It is very far away. And planets move relative to it, not vice versa; if we collided it'd be more accurate to say the Earth was doing the crashing."

Your sister said that. It doesn't really seem like a meaningful difference.

"It mostly comes up when predicting the motions of other planets. All the planets near here are in elliptical orbits around the sun."

- we do not have ...any of that, I don't think.

"What do you have? How did you get here?"

I have no idea how we got here.

We have Arda. It doesn't move, or at least I can't think of anything for which it's useful to model it as moving, and it is lit by Trees.

"Here trees don't give off light."

Most trees don't, but those two were designed as lighting.

"By..."

Yavanna, the Vala of growing things.

"And a Vala is..."

The creators of the world and the instruments of Eru's will within it. Osanwë also conveys that this is the standard answer. They're magical and powerful and don't usually assume physical form and live in different remote parts of Valinor. They don't do very much now but when the world was young they did lots of design things and fought a war.

"Okay. - how old is your world now?"

A few thousand years old? I don't think they kept good track at the beginning.

"Okay... uh, anything Alli wasn't able to explain you want me to take a stab at?"

The process by which your animals turn into people, and why this is not a reason not to hunt. It really does sound like a reason not to hunt. 

"That takes millions or billions of years. It doesn't happen to individual animals, it's a gradual, generational thing."

Oh, good. ...that's a really long time. I bet my brother could do it in a thousand.

"It... might be possible to deliberately breed animals for intelligence and get people out of it but it's never been done and a thousand years seems like a really short time frame."

He can talk to them! He's the only person we know of who can do that. And as he talks to them, the way they process things gets more people-like and if he did it for a thousand years or so it would not surprise me if they were people? He wouldn't, though. It's hard to know the best kind of environment for a child like that.

"...okay. Do you have other questions?"

The powers are only for twins, and your creators started doing that without an announcement somewhat recently?

"No announcement accompanied the spontaneous commencement of twins acquiring superpowers, nor is it clear from where or from whom such an announcement would have come. It was about fifty years ago. - local years are defined as the time it takes the Earth to make one circuit around the sun, which is 365 days and change, a day being twenty-four hours."