Ice Princess and Flame Brain have younger sisters?!

Flame brain (Natsu) has a younger sister named Jazz, she is pretty much the same as him except a lot more reckless. Ice princess (Gray) also has a younger sister, her name is Kiva, she is an ice make as well but she is not as easily riled up like Gray. Kiva and Jazz get abandoned by their brothers as kids and meet up with each other to find them not knowing the relationship betwbeen their brothers.

What will happen? Will they two boys fall in love or will they fight to keep their sisters safe?