Hi, I need help with objects when I put them on stage if I set different size to sprite to do to keep this fixed size? And there is a way to create the object once and use it in various scenes? And collisions are run between objects that are in the same layer? And as it does to rotate an object at a fixed point without turning it exits the scene are these my main doubts among many XD thank you to anyone who can help me !! 
I don’t think there is such a way. But you can always use external layouts and selectively keep objects you want to! check it out in the documentation. It might help with your problem of keeping the size too
If you are really keen about the size you can always resize the original sprite to the required and then use it in your project! 
Not necessarily in my experience
Thank so much aryanagal - you help me! God bless you ;]
Our GDevelop family welcomes you!! 