They also have over a million mutants who happen to have very convenient mutations, so it is not unreasonable that whatever they would need to travel to Earth, they have.
I am not thinking too much about it, from Magneto just coming up with this plan a few days before the Gala (which means this was never something the Gala was planning on show off) to everyone just knowing how to use their powers for this specific task (they come off as magic rituals) to a population who has been enslaved for generations are a bunch of conquerors (and their corrupt leadership is in exile), the story reasoning for all of this is just slapped together to get it over with an on to the next thing, which may or may not follow logically from anything or nothing written here or before.