Hello @Patrick_GABLE
If you have a little time to train, try to learn how to make a skeleton assembly and design part. Or to get closer to this method.
This will save you from constraints carried out in an empirical or even anarchic way.
Happy learning
Hello @Patrick_GABLE
Nice that your problem is solved. Remember to click on the green checkmark to validate the best answer and move the subject to solved?
Good luck.
Thank you FRED78 for the idea of the skeleton design. I'll follow the tutorial below that I found on this forum. 
Skeleton design tutorial
We had discussed it at length on this forum. There must be one or more topics talked about on the forum. And I seem to have put assemblages as an example.
Below is a playful example on a simple piece.
There are two methods:
1 By integrating a skeleton into the parts
2 As an external reference in an assembly, the part is created by reworking by projection in a sketch.
02-methode.7z (678.1 KB)
Ah, ok. From what I read, it was my answer that solved the problem, but I guess @Patrick_GABLE checked the first answer by default. It's very sad 
Sorry Sylk if I offended you, but if I identified the first answer and in the state that of sbadenis it is that it clearly answered the title and subject [ Function " Move / Copy bodies" greyed out ]. So it's not by default 
Now you have indeed brought me a solution to my problem, perhaps misidentified by mistake of youth, but I have clearly notified your proposal which has helped me out. 
Readers will sort through all the answers provided by each one and take advantage of them if necessary. 
Don't worry, to hurt me up you'll have to go back 
In this case I present you with all my confusions.
Be careful, silk wrinkles easily