Forbidden Waters by Rosie Wylor-Owen

“If we don’t break the phoenix’s curse, we’re all going to die.”

The entire island of Dusk has turned on the Arrowood and Everhart families. After a phoenix egg is destroyed in the name of their feud, its mother cursed the population with a magical illness that threatens to kill them all.
Maeve Arrowood and Ben Everhart kept their love for each other secret but if they plan to break the phoenix’s curse, they will need the help of their friends and family. When Maeve discovers a clue to the location of a time-travelling pirate ship in her late mother’s diary, she and Ben track it down to see if they can change the past.
As they find themselves bouncing through time with no direction, Maeve and Ben discover that the only way to save the island is to break their own curse.