Yes. But I am talking about what works in native Blender with no plugins. You don’t need to solve this with a plugin. You never mentioned anything about a plugin. That is another piece of information. So to remain scientific about this, I recommend resetting to Blender defaults and follow my instructions.
The interchange between Blender native defaults and Unreal Engine works perfectly fine. You just have to understand the very basics and then proceed.
So the reason you are confused is because you have many moving parts. And conflicting information.
Keep in mind that I do this for a living. Exporting assets to game engines with and without animation using the fbx exporter from Blender. Just recently I rebuilt a scene in Unreal that my team had animated in Blender. So this information is very fresh on my mind.
Just from your description, I can see you are trying to go too many directions at once. And also there may be other things that are entered into this equation.
First and foremost is the file format.
.fbx works completely differently than Alembic for instance. You approach these completely differently.
gltf is something else entirely.
I would say keep it simple. First just get fbx to work with a simple one character or object. And verify the scale is correct on both sides.
And the gradually build from there. You can either build a scene in Unreal with many parts, or use Datasmith to import larger scenes which is what it was designed for.
For animation I would stick with tried and true .fbx. It works very smoothly for this. And in my opinion the best option.
As promised, I will get around to making a video on this.