Beaches are the quintessential natural light portrait location.  Indeed, their gentle post-sunrise and pre-sunset light is soft and golden -- flattering to all skin tones.  And, the neutral tones of the water, sky and sand make for a timeless backdrop.  In the group portraits below, the dunes were the only prop available to layer my subjects and add dimensional interest to the final images.  In the individual portraits, I shot with a 200mm L-lens  "wide open" with an aperture of f/2.8 to create a dreamy, softly blurred backdrop.  Group photos require a wider angle and higher depth of field.  

Attire is key in any group portrait.  I recommend avoiding the "matchy-matchy" look of the 1990's and the crisp white shirts with khakis look of the 2000's.  Avoid competing patterns and choose a few complementary colors for everyone to choose from.  For summer beach portraits, my favorite is navy-light blue-grey-tan combinations.  

The ocean isn't always the most interesting background for your picture.  Look for opportunities to utilize the sky, and place the setting (or rising) sun in the top corner for group portraits.  Experiment with backlighting by placing the sun directly behind your subject.  Expose for the sky if you want a silhouette (2nd photo below) or spot meter for your subject to keep faces properly exposed (3rd photo below.)