When the Avengers return to the big screen on May 1 in Avengers: Age of Ultron, they'll be joined by a couple of newbies -- Scarlet Witch (Elizabeth Olsen) and Quicksilver (Aaron Taylor-Johnson), siblings (and Eastern European travelers) who posess the sort of powers we haven't yet seen in the Marvel Cinematic Universe.

But who are they and how will they fit in with Iron Man, Captain America, Thor, Hawkeye, Black Widow, Hulk and the rest of the team?

Fandango had the chance to speak to both Olsen and Taylor-Johnson when we visited the Age of Ultron set a few months back. Here's what we learned about the brother and sister team (aka "the twins") -- from what they were doing before we meet them in Age of Ultron to the very different approaches each took while preparing to star in one of the biggest superhero sequels ever.

First up... a little more on the twins.

5 Things You Need to Know About Scarlet Witch (aka Wanda Maximoff)

Hometown: Prior to Age of Ultron, Scarlet Witch and Quicksilver traveled around Europe, eventually settling in the fictional city of Sokovia. They don't have any permanant home, though, as Olsen describes the duo as having a "kitschy vagabond feel" to them.

Special Powers: She can harnass energy and use it to create explosions. When we meet her in Ultron she's still learning what she's capable of and how to take command of it.

"I can control energy. I can manipulate energy away," she says. "I am able to go into someone's head and they'd never see. I can feel and see what they feel and see, so it's not just me manipulating them. For her everything that someone else could feel -- like their weakest moments -- she physically goes through that same experience with them, which is pretty cool."

Favorite Avenger: Kinda hard to top the dude in the iron suit. "My favorite -- just as a fan -- is Iron Man," Olsen tells us. "Those are my favorite films and that's how I got into the Marvel world and became a fan myself."

Good or Bad: When we first meet Scarlet Witch and her brother Quicksilver, we're not so sure which side they're actually on. "I think we can know so many things about someone but not know maybe what they're capable of, in terms of being bad or good," Olsen says. "And I think everyone has maybe good intentions, but they do bad things."  

Insider Fun Fact: Speaking of doing bad things, in the movie Scarlet Witch uses her powers to get inside many of the characters' heads, exposing their darkest fears while also forcing them to confront what they are. "She's able to bring out the worst in us," Mark Ruffalo (Bruce Banner/Hulk) says. "It's like Sid and Nancy. She's the Nancy. She's everyone's Nancy."

5 Things You Need to Know About Quicksilver (aka Pietro Maximoff)

Brother of the Year: Scarlet Witch and Quicksilver are very different from that other pair of famous Marvel siblings, Thor and Loki. For one, they actually look out for each other. "He's protective of her in a physical way and her more in a psychological way," Taylor-Johnson tells us. "So we try and embrace that [in the movie]." 

Special Powers: Dude is fast. Real fast. He can disorient his adversaries with his super speed, or use it to steal from a local market so he and his sister have dinner for that night.

Favorite Avenger: When revealing his favorite Avenger, Taylor-Johnson recalled a scene where the entire cast was together in one room. A quick glance at everyone in their costumes helped answer that question rather easily. "The only one who is actually otherwordly is [Chris] Hemsworth," he notes. "I mean the size of his arms are the size of my thighs. Everyone is charming and brilliant, but when you look around the room [and you see Thor], you go, 'Yeah, now that guy is definitely a superhero!’"

How He Fights: Running at an incredible speed is one thing, but how does Quicksilver throw down when the Avengers are in the middle of a brawl with Ultron? "Because I literally run at super speed, usually it’s an elbow or a shoulder that will send someone flying," Taylor-Johnson says. "It’s the force of impact with my powers. It’s only when I’m slowed down that I’m very vulnerable."

Insider Fun Fact: When he signed on for the role, Taylor-Johnson had two specific requests for director Joss Whedon: "To keep the white, silver hair [from the comics], and to embrace the roots of where he's from, being Eastern European."

They're Not Your Typical Superheroes

Yes, this is true, but it may not even be fair to call the siblings superheroes at all because, well, technically they're not like any of the other Marvel heroes we've met on the big screen so far.

Instead you can refer to them as "miracles," as the villainous Baron von Strucker does at the end of Captain America: The Winter Soldier. (You can't call them "mutants" because 20th Century Fox, which owns the film rights for the X-Men, is in charge of that specific term -- despite the fact that the siblings' father is X-Men's Magneto, according to the comics.)

Or, perhaps, they're our first big-screen introduction to Marvel's Inhumans.

The Inhumans are a genetically advanced race of superhuman individuals whose powers can only be unlocked through a process called Terrigenesis, which allows Inhumans to inhale the mist of Terrigen Crystals, thus unlocking their special powers.

So what does this have to do with Scarlet Witch and Quicksilver? When we first met them at the end of Captain America: The Winter Soldier, they were being held captive by Baron Strucker, who was in possession of Loki's scepter and had used it on the brother and sister during a series of freaky experiments. Could he have unknowingly unlocked their powers with the scepter? If so, does that make them the first big-screen Inhumans?

You'll have to wait till Age of Ultron to answer some of those questions. In the meantime, Marvel has scheduled an Inhumans movie to hit screens on July 19, 2019.

The Crazy, Unexpected Ways They Trained to Become Marvel's Newest Avengers

Scarlet Witch

So how do you prepare to play a character who channels energy from her hands? You dance, of course!

Says Olsen: "We started off with Joss [Whedon] having these ideas based off images in the comics of what the hand gestures would look like or [what] the arms look like. And then I worked with a dancer, Jenny Wade. She's a choreographer and dancer -- and the two of us would get locked up in a room together and we'd move and try to figure out what looks strong; where the energy comes from. It's funny because everyone else is doing these big stunt practices, and I'm just pretending to make things shoot out of my hands. I don't feel as tough as everyone, but it's super fun."

Quicksilver

One thing we learned from Taylor-Johnson on set is that it took a lot of practice to make his Quicksilver...well, quick.

To make it look as if Quicksilver can run as super-fast speed, they tested out a couple of different things. For one test they put Taylor-Johnson in a harnass strapped to a "giant running machine," but according to him "it didn't really give a sense that anything was traveling. When you played it back, it looked too clean and neat."

For the next test, they went on a road and filmed Taylor-Johnson from a moving truck as he sprinted down the street. "They're on a truck and I'm sprinting for 100 meters," he says. "The crazier we got -- with me ducking and diving -- when they sped that up, it had a much more interesting flavor to it."

That's all fine and good... but could he beat the rest of the Avengers in a foot race? 

"I mean, it'd be pretty embarrassing if I said I wouldn't win," he jokes. "If they're all in their costumes, then definitely -- for sure!"

For more on our trip to the set of Avengers: Age of Ultron, check these out:

The First Round of Our Top-Secret Set Interviews with Robert Downey Jr. and Mark Ruffalo

8 Revealing Quotes from Avengers: Age of Ultron Director Joss Whedon

The Second Round of Our Top-Secret Interviews with Chris Evans and Jeremy Renner

6 Things Thor Wants You To Know About Avengers: Age of Ultron