Thanks!

In the world of ponies there is already a portal-mirror to the world of people. I think there are still different portals. Moreover, Twilight loves to play with magic.

Since the Pink Diamond is Pink Quartz, I think she only pretended to hold the gems as hostages.

I think she noticed that the organic form of life is trying to steal stones and move them to another place. Moreover, she noticed that Sweetie Belle is reasonable. So Pink Diamond decided that it would be better for her friends to go to another world, to interesting and kind forms of life, than to be in prison.

However, I think Rarity did not know that she stealing living things. She simply decided to “borrow” the beautiful gems that flew in the air without much purpose.

When this couple returns home, I think they will find that they have taken the aliens with them. And, of course, they will make friends with the gems and will help them in the fight against their homeworld! :З

Sorry if something is misspelled. English is not my native language(