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They became one with Bane and died

Short answer is, we don't know. I don't think they were being raised to be Inquisitors. IIRC, Dave Filoni once said something along the lines of, "Their fate is something that we can't show on a children's cartoon," implying that Sidious was experimenting on them. In all likelihood, they were resources he was using to try and figure out how to clone Force sensitivity for the sake of becoming immortal.

He was probably raising them to be his personal consorts. To torture them for shit and giggles.