Pre-heat your grill on high.
Place the par-boiled potatoes in a single layer in the bottom of a large roasting pan.
Layer the onions, sausage, and corn, then the shrimp, mussels and clams.
Mix the Old Bay Seasoning into the water and pour the water and wine over the contents of the roasting pan.
Lay the sprigs of parsley on top.
Then set the lobsters on top of this mixture. Don't worry if the mixture is mounded up above the top of the pan.
Cover the roasting pan TIGHTLY with heavy-duty foil and set the pan on your pre-heated grill. (I use two fairly large pieces of heavy-duty foil crimped together. This makes a large enough piece to have plenty of overhang to get the seal tight so the food can steam.)
Close the lid and cook for 20 to 30 minutes over high heat. The food is done with the clams and mussels have opened.