Nowadays, there are plenty of websites in which you can easily find the best flight for you by inputting your departure day, return day, destinations and timings.
They automatically give you all the best offers with different flight companies, so you can easily find the best ticket for you at the best price (remember that as soon as you buy the ticket, respect your departure date, better price you will have).
Be sure to know the day, month, island airport and timing of your trip in order to join your group.