Good story, or not? Please comment?

In a medieval style world, in a place where something called the Plague is killing everything, sisters Tourmaline and Lazuli (Lah-Zoo-Ly) live with their father, Tor being the tom-boy, and Lazuli is the romantic one. The night their father dies, a mysterious stranger approaches them, telling them that they have powers, They both dismiss him as crazy, they go to live with their grandmother, whilst they are their they find out that they do actually have powers, and that their aunt is actually a demon who wants to kill them. Lazuli wants to use her new psychic abilities and ability to strenghten the mind and soul for good things, and find a cure or stop the Plague, whilst Tor wants to use her new super strength to fight in a colluseum-like structure and defeat people. They separate, and after a while they realise that there are people who want to kill them, they become friends again, and fight the bad guys