Wear whatever you would like to. There will be photos taken so dress to impress a little bit at the very least! For Guys: Slacks and a button down is a safe bet. Linen if you're feeling festive For Girls: Dresses and jumpsuits work well!
Plan to arrive 15 minutes early. Coconut Grove is on the beach on the Fairmont Orchid property so it should be easy to locate.