Dare.

"Dare, of course" I said.

"Okay then" she said "we'll we're already naked and both you're siblings have seen at least one of us naked".

"So?" I asked, dreading here response.

"So, I think it's about time we step this game up a notch. We can just get rid of the truths, we're not doing them anyeway and move on to more daring stuff and with you're parents away there's no risk of getting caught by them".

"So what did you have in mind?"

"Here's the game, you have to get a selfie with your sister and I have to get one with your brother. They dont have to know your there, they can just be in the background and we have to be naked but they don't have to. However, if they are naked you get to make the other player do a forfeit. Got it?"

"I think so" I said. I wasn't particularly keen on being naked in the same room as my sister again, nevermind trying to catch her naked and photograph it. At least she didn't have to see me naked this time. "Alright then lets go take some photos".