Prepare the seafood. Peel and devein shrimp. Cut the Mahi-Mahi into cubes to somewhat match the size of the shrimp for even cooking.
Make the marinade: put the squeezed juice of 2 limes with the olive oil and garlic in a large bowl. Mix thoroughly to blend and add some salt and pepper. Put the prepared seafood in the marinade and stir gently until it is completely coated. Cover and chill for 1 hour.
Remove seafood from the marinade and thread alternately on skewers. Grill or broil , turning occasionally, until cooked and tender. Approximately 5 minutes. Baste with more marinade if the pieces appear to be drying out.
In the meantime make the jalapeno butter; blend the softened butter with the chopped chiles and thoroughly blend.
Arrange the skewers on plates on a bed of rice. Pat chili butter over all. Scatter with torn cilantro leaves.