Bring an 8- to 10-quart pot of water to a boil, then plunge 2 lobsters headfirst into water and boil, covered, 6 minutes from time they enter water.
Transfer with tongs to a shallow baking pan to cool, then boil remaining 2 lobsters.
When lobsters are cool enough to handle, twist off tails, claws, and knuckles and remove meat, discarding bodies and shells.
Cut tail meat crosswise into 1-inch-thick slices. Put lobster meat in a large bowl.
Bring wine, water, and 1/2 teaspoon salt to a simmer in a wide heavy medium pot.
Add scallops and poach at a bare simmer, uncovered, until scallops are just cooked through (opaque), 3 to 4 minutes.
Transfer with a slotted spoon to bowl with lobster.
Return liquid to a simmer over medium-high heat.
Add mussels and cook, covered, stirring occasionally, until mussels just open wide, checking frequently after 4 minutes and transferring to bowl with seafood. (Discard any mussels that remain unopened after 6 minutes.)
Strain cooking liquid through a sieve lined with a dampened paper towel. Rinse pot, then return liquid to pot and boil until reduced to 1 cup, about 8 minutes.
Heat oil, garlic, vinegar, 1/2 cup reduced seafood liquid, and 1/2 teaspoon salt in a 1 1/2- to 2-quart nonreactive saucepan over medium-low heat, stirring occasionally, until warm, about 2 minutes.
Add tomatoes and cook until they just begin to wilt but still hold their shape, 3 to 5 minutes.
Pour hot vinaigrette over seafood and stir gently to coat. Marinate, covered and chilled, at least 2 hours. Bring to room temperature, about 30 minutes, before serving.
· Lobsters can be cooked and meat removed from shell 1 day ahead, then chilled, covered.· Seafood can be marinated up to 6 hours (any longer and texture will deteriorate).
