Twin Theory Edit
Under the assumption that the dreams the fleshchild haves has some origins from the original human their stolen brain came from, we can assume that the original brains came from two conjoined children. Vice and Visi (as humans) were born conjoined twins and were separated, both still have memory of this.(Mutilation effect, conjoined effect)
As there is constant symbolism of their duality, we could assume that they were not only separated, but separated from themselves for most of their lives. It symbolizes their constant longing to be with eachother again as brother and sister. (Where the doll effect is found, both representations of the twins are next to each other, and could show that the both remember playing together.)
Perhaps both of the human twins requested to donate their organs, and their brains coincidentally ended up next to eachother in the lab.