They even work to mess with perception of time, as the kids advance the date on the lodge’s clock.
The act of gaslighting is foreshadowed in The Lodge when Aiden straight-up uses a gas-powered heater to try and warm up the titular dwelling, as it’s following that scene that everything starts to get “weird.”
The siblings drug Grace’s tea, which gives them time to take everything in the cabin (including all of the food) down into a storage space.
They are also responsible for shutting off the power and water, and while Mia maintains a working cell phone – which she uses to stay in contact with her dad – it winds up being another gaslighting tool, as they convince Grace that it’s dead and that Mia is just pretending to have a conversation.