The Hadids seem like they're a pretty close family, especially sisters Bella and Gigi. The two models are close enough to have worked together for the March 2018 issue of British Vogue. Bella and Gigi both have their own cover in addition to a joint cover, all photographed by Steven Meisel. Oh yeah, that joint cover features the sisters hanging out together in the nude.
The cover has received a lot of negative feedback for the sisters' nudity and pose.
Now, it could very well be that the Hadids were covered up to some degree with pasties and thongs, which were airbrushed out. Or the sisters went totally nakey as the day they came into the world.