I started reading a book in school about siblings or twins — it was a brother and a sister. One was learning elemental magic, maybe both were, but they had to run from their home for some reason. The title has something about alchemy or potions or cauldron on it, and had either a potion or a cauldron as the main art piece.
The Alchemyst (2007) by Michael Scott, first book of the "Secrets of the Immortal Nicholas Flamel"?
- twin protagonists, both learn one elemental magic per volume
- alchemy-related title
- potion on the cover art
Nicholas Flamel was born in Paris on 28 September 1330. Nearly seven hundred years later, he is acknowledged as the greatest Alchemyst of his day. It is said that he discovered the secret of eternal life. The records show that he died in 1418. But his tomb is empty and Nicholas Flamel lives. The secret of eternal life is hidden within the book he protects - the Book of Abraham the Mage. It's the most powerful book that has ever existed. In the wrong hands, it will destroy the world. And that's exactly what Dr. John Dee plans to do when he steals it. Humankind won't know what's happening until it's too late. And if the prophecy is right, Sophie and Josh Newman are the only ones with the power to save the world as we know it. Sometimes legends are true. And Sophie and Josh Newman are about to find themselves in the middle of the greatest legend of all time.
Found by memory, I used to read those in high school.