In the film Grindelwald tortures Newt to provoke Credence into releasing his obscurus. I want a scenario where Grindelwald captures both Newt and Credence, and keeps Newt around to control Credence. Newt-torture could happen either as motivation (do what I want and I'll stop hurting him), or as punishment for Credence's failures, or both.

I'm not picky about what kinds of relationships exist or develop between any of the three. No permanent mutilation please, but sexual abuse/torture is more than okay.