To open these chests you will need a group of 5 people. Class and gender doesn't matter.
Note: Each chest's contents will be gender specific depending who opens it.
Once you have assembled your group head to Paradise 1 or Paradise 2 and begin to search the waters.
Once a group member gets a popup they should call out the location to their group. Closing the popup is harmless and it will still be there when you refresh (F5).
Each chest will have a different instruction to open it.
Your group must stand in the shape that it requests in order to open it.
Here are the various shapes it will ask for, as well as the formation for your group:
The person at the centre of the shape will recieve a random reward based on their gender: