Any brothers and sisters or siblings skinny dip with each other?

I've had some friends mention to me how they went skinny dipping with their sister and brother in-law before with their wife. Like a brother and sister went skinny dipping together with their spouses. Like it was normal. Part of me says it's fine if it doesn't get sexual. Anybody have stories like these or something similar?
Any brothers and sisters or siblings skinny dip with each other?
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