There is no implication or indication that Luke and Leia ever slept with one another, even before they knew they were siblings. What made Lucas decide to change Princess Leia from Luke's love interest, whom he passionately kissed, to his twin sister? How would Star Wars be.
Now, to help ruin the childhoods of that many more people, I offer for posterity my proof that Princess Leia had sex with both Luke Skywalker.
When Skywalker dies—or becomes one with the Force or whatever—in The Last Jedi, did he shuffle off this mortal coil as a virgin? If Luke Skywalker died a virgin, I have no problem with that (unless he was some sort of 4chan incel, which is an entirely different conversation).
The son of Anakin and Padmé Skywalker, also the brother of Leia Organa. Sex Move: While wearing a glow in the dark condom, take your dick out and slap.