*PLEASE REFRAIN FROM WRITING ANYTHING WHICH IS NOT BASED ON THE QURAN.
*PLEASE IGNORE THE CONTEMPORARY TABOO ABOUT INCEST WHEN REPLYING.
*I AM NOT INTERESTED IN INCEST SINCE I WAS BRAINWASHED THAT IT IS TABOO, I DON'T GET TURNED ON BY LOOKING AT RELATIVES. THIS THREAD IS ONLY FOR DISCUSSION ABOUT WHAT OUR RELIGION ALLOWS.
*PLEASE DO NOT DISCUSS ABOUT THE POSSIBILITY THAT SUCH ACTS WILL LEAD TO INCESTUOUS PENETRATIVE SEX. IT IS NOT A FACT, AND THE POSSIBILITY ISN'T GROUNDS FOR FORBIDDING IT.
I hope we can have a mature discussion after I made those things clear.
As I understand from the Quran, women should cover their bosoms and genitalia in front of non mahrams, while males should only cover their genitalia. (I am not even sure about the genitalia parts...)
Since there is no limitation, we can understand that it is allowed to be fully naked in the sight of siblings, parents, children, etc. It is also allowed to touch and kiss mahrams anywhere (since it is not prohibited) except from the genitalia which is reserved for spouses and MMA(ma malakat aymanukum).
My conclusion is that there is no prohibition of incest as long as there is no penetration (or any kind of stimulation of the genitalia by the touches of the mahram). So kissing, making out, cuddling, and even mutual masturbation with a sibling is not prohibited by the Quran.