[Coffee.]

I answered "No siblings ever do this" because I think these actions are very uncommon in most developed nations with a population base. In the old days, people often mated with their siblings because of, well, lack of opportunity, but now, I do not think this is common at all. Most of the time, incest is meaning rape. You did not include two siblings masturbating together, and as I have never done this, I can see this happening and that wouldn't be far fetched. The rest of this, very uncommon, and usually unwanted by one party.