I'm afraid H/C Ex isn't really set up for specific sex scenarios. Generally what people are asking for is fic about relationships, romantic/sexual or friendship, with all H/C related prompts.

Specific sexual scenarios like gang bangs are probably better suited for exchanges set up for them.

For this, I'll all the example to the rules, using something like "(Peeta & Gale)/Katniss" would be a short way of writing "Peeta/Katniss and Gale/Katniss but not Peeta/Gale"

I think for your scenario since you want all the characters having a sexual relationship with Hux, parenthesis would be best. I can edit that for you.