In a medium bowl, combine the crabmeat, shrimp or lobster, orange juice, 2 Tbs. of the cilantro, 1 Tbs. of the chile, the olive oil, chipotle powder, and 1/2 tsp. salt. Let the mixture sit for 20 minutes.
Using a mortar and pestle, or the blade and side of a chef’s knife, mash the onion, the remaining 2 Tbs. cilantro, the remaining 1 Tbs. chile, and 1/2 tsp. salt to a paste. Leave the paste in the mortar, if large, or transfer it to a serving bowl.
Halve and remove the pits of the avocados. Use a paring knife to score the flesh in a 1/2-inch crosshatch pattern, being careful not to cut through the skin. Use a spoon to scoop the avocado into the bowl.
Along with the remaining cilantro and the lime juice, mash the avocado gently with the pestle or a fork, leaving some chunks. Using a slotted spoon, add two-thirds of the seafood mixture to the bowl. Season to taste with more lime juice, salt, and chile. Use the slotted spoon to top the guacamole with the remaining seafood just before serving.