Ether constructs ( 3 SB theory)
I’m sure this idea has been discussed before but I really do think this is the most likely scenario.
For those who haven’t heard it yet,
Basically the idea is that the original SB was a robotic intelligent construct but when she splits herself into 3 they won’t into mechanical body, but body made from Ethereal made to resemble humans.
This was done using the power of the creator, as we can see in both Sarah and mimic ethereal’s that Ethereal can resemble humans and even inherit memories.
I think this is the most probable scenario, as we don’t really see any hints of the 3 SB being mechanical.