Good book idea or basic? Any tips or suggestions?

“” means that I haven’t figured out a name yet

Sybil and Silius at 18 year old royal twins, whose lineage has the power to control fire(?). At the age of 5, their kingdom was overthrown by power-hungry King “”. Their parents brutally murdered, Silius led Sybil to safety to a small city where they took refuge at an assassins den. The king went on to conquer all the kingdoms on the continent. They trained, doing jobs to earn their keep. Upon turning 18, Silius was now able to take the crown, promising Sybil they’d rule side by side. Sybil agrees. The twins have little left in their court so they go separate ways to find other lost royals. Sybil goes Southeast coast to the old kingdom “” in search of Princess “”, a girl who’s lineage controls water. Along the way, she meets “” an almost-ordinary boy whom accompanies her. The princess gathers up her resources and agrees to fight alongside the twins. Silius goes on his own journey to the north west to the mountains and forest searching for the lost Queen and her Son, who controls earth. They too join the rebellion cause. A princess from a small kingdom hears of the news and makes contact with Silius, to his surprise, the Asian pacific princess has an abundance of resources, and the ability to control weather. The world had long since believed the ability had died out. The two connect (and I’ll leave the rest to the imagination for now). Upon the fact the twins have the ability to control fire, they also have telepathy in which they use to communicate despite all the allies they’ve obtained, they are greatly outnumbered. Silius meets Sybil on the coast in which they decide that they must ally with their old enemy, young King “”. They travel the seas and ask for the Kings help. He agrees only so long as Sybil marries him to unite the two continents. The ordinary boy and Silius beg her not to, but she does what she thinks is best for her Kingdom and agrees. The King gives them plenty of soldiers and an armada in which they use to defeat and avenge the murderer of their parents. Each kingdom is given their freedom. Sybil returns the her soon-to-be-husband. She gets cold feet on her wedding day, the humiliated king throws her ordinary boy in a prison vowing that he will only live if they become husband and wife. With no other choice, she marries him. Sybil now trapped in the evil King’s clutches.

(End of book 1?)