I created a video about my problem:
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Algorithm:
Given a group of objects and a goal.

STEP 1 - Find the center of the group.
STEP 2 - Find the path from the center to the goal (it's a list of points).

STEP 3 - For each object, send it to its formation position (relative to group's position).
STEP 4 - Move the objects.
STEP 5 - Repeat STEP 4 If at least one object moved.
STEP 6 - If the goal is not reached, grab the next position of the path and go to STEP 3.

STEP 7 - End.

As you can see it's not perfect, If you have any idea how to improove it, I would thank.

Are you using A* or steering?

Bi-Directional A* with Manhattan Heuristic

I can't find any papers about this subject...

Hi

STEP 3 - For each object, send it to its formation position (relative to group's position).[/quote]

What about making the group moves as one object in the open area , and every object will move on its own when facing an obstacle ?
The way your objects move reminded me of the old typewriter , the objects move few stpes up and right and then return the straight line of the path and so on ,
Here is a video where the wole group moves / rotates as a singel object (like a rectangular object )
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Hope this helps .