Put the shrimp and scallops into a large Ziploc freezer bag.
Mix all other ingredients in a bowl until well combined.
Pour ¾ of the marinade into the bag with the shrimp and scallops, reserving ¼ for basting.
Seal the bag, place it in the refrigerator, and marinate for 15-30 minutes, turning occasionally.
Soak wooden skewers in water for at least 1 hour, then remove and pat dry with a paper towel.
Sprinkle parsley, dill, chives, onion.
Drain and discard the marinade from the shrimp and scallops.
Thread the shrimp and scallops onto the skewers, alternating between them.
Preheat the grill to medium-high heat.
Grill the skewers for 3-5 minutes per side, basting with the reserved marinade.
Cook until the shrimp turn pink, the scallops are opaque, and both have nice grill marks.