This is impossible by design currently. It goes down to how scripting works in Godot in the first place, as there is physically no way to inherit C++ classes directly with a script. So what happens is, any script extending an object will be attached to that object, and there can be only one. Even basic classes are just
References with a script on them, but from the scripting world you mostly don't see this due to how it's integrated.
I would even go further and say, this is not only a Godot thing, I've actually never seen engines have this work perfectly, unless when the script language is the same as the engine language.
extends is a "lie" ^^
So you have to live with it for now, probably change a bit the way of thinking...
There has been a long discussion about this: https://github.com/godotengine/godot/issues/6067