Those were Quicksilver and Scarlet Witch. In the comics continuity they're the twin children of Magneto from X-Men, and were once bad guys but eventually reformed and joined the Avengers. Both Fox and Disney own their rights. They're going to be in the next X-Men movie as well, but played by different actors. It's weird. In the Marvel/Avengers movies, they're not allowed to call them mutants or refer to Magneto because of the rights, but they're mutants in the comics. Quicksilver moves extremely fast, and Scarlet Witch has the power to alter reality, though she can usually only control it enough to make minor alterations. I don't know if her power will be the same in the movies.

They might be under the control of the staff. That was Loki's staff they showed before revealing the twins, and Loki used it to mind control Hawkeye in the Avengers movie.

Also, I think Doctor Strange is going to show up in one of those Netflix Marvel shows that's coming next year or whenever it is. But I'm not sure about that.