Well it’s possible, you could have a bunch of different skeleton hierarchies using one skeleton. The skeletal meshes would then use the bones they need. I think it would become pretty hard to use though with a bunch of control rigs in the same thing. Or maybe you could export with the massive skeleton and just animate using another rig that fits the character you’re working on, then retarget to the actual character.
You can’t really share animations between them if the characters are so different though so maybe there’s not a lot of benefit to having a shared skeleton.