These are family-friendly movies that will never make overly direct references to sex (much less show it take place). There is no implication or indication that Luke and Leia ever slept with one another, even before they knew they were siblings.
While Return of the Jedi would ultimately reveal them to be siblings, A New Hope implied Luke's attraction to Leia throughout, while the two kissed multiple times in The Empire Strikes Back, with further romantic moments ending up on the cutting room floor, as seen in the movie's deleted scenes.
Following his nearly fatal encounter with a wampa on Hoth in The Empire Strikes Back, Luke Skywalker is rescued by Han Solo. In a medical center shortly after, Princess Leia checks on a recovering Luke, and in an effort to make Han jealous, she kisses the bedridden hero and walks away.
Not as obvious as you'd think. Leia kissed Luke three times: once on the cheek “for luck” right before the swing across on the first Death Star, and once rather forcefully in the sickbay on Hoth (when she's trying to make a point to Han.)
Undoubtedly, his greatest love was with a character named Mara Jade. Mara is a strong character as a part of the expanded universe of the Star Wars Legends series of novels. Their love is so strong that Luke winds up marrying her, and she bears a son that they name Ben (not Ben Solo).
Presumably, the scene was simply meant to make Han jealous. Still, Luke looked very thrilled by this unexpected turn of events and Leia seemed to consider both men romantically, though the sexual tension with Han was admittedly much more palpable.
It was revealed that Luke and Leia were siblings, and the kiss in "The Empire Strikes Back" was part of Leia's attempt to make Han Solo, with whom she had a romantic relationship, jealous. Han and Leia were fighting at the moment they kiss, and Leia kissed Luke to make Han jealous.
The students concluded that Luke is therefore 1.75 years younger than Leia, possibly rendering them the first twins ever to have over a year between their ages.
In the 2015 film Star Wars: Episode VII – The Force Awakens, it is revealed that Han had a son named Ben with Leia. The family breaks apart following Ben's descent into the dark side as Kylo Ren, with Leia and Han separating. Luke is not revealed to have any children.
Darth Vader only learned he had a daughter in Return of the Jedi - but there's no evidence he realized she was Leia before his death and redemption. Darth Vader may have never known Princess Leia was his daughter in Star Wars and never cultivated a relationship with her, even when he was a Force ghost.
In between escaping the the trash compactor on the Death Star and returning to the Rebel Base on Yavin IV, Han Solo and Princess Leia did, in fact, sleep together during the events of Star Wars.
To get more controversial, In The Empire Strikes Back, Luke and Leia go from a peck to steaming mouth type of kiss so Leia makes a point against Han Solo (Harrison Ford).
Luke and Leia only discovered they were twins in Return of the Jedi despite being Force-sensitive. Could they have known earlier in Star Wars? Luke and Leia never sensed that they were twins until Return of the Jedi despite both being sensitive to the Force.
Alderaan's princess knew she had been adopted by Bail and Breha Organa after the Clone Wars, but she had no idea who her parents were. That was until Luke Skywalker told her the truth - that he was the son of Darth Vader, and that she was his sister.
She assures him the conversation was about Luke learning that she is his sister, but the jealousy alone is enough for Leia to know that her love for Han is reciprocated. After avoiding dropping the L-bomb, Han finally tells Leia that he loves her when she saves him from some Stormtroopers.
Did Leia know Luke was her brother when she kissed him?
Honestly, I only find the kiss Leia gave Luke at the beginning of TESB awkward because she was trying to make Han jealous. The one she gave Luke after she and Lando rescued him is understandable, given how Luke was injured. She didn't know that they were related.
In hindsight, Luke had the luxury of carrying his father's real last name because he was a nobody hidden in the Outer Rim Territories. Leia, on the other, was adopted into a well-known and prominent family, hence why she was given the name Organa.
There is no implication or indication that Luke and Leia ever slept with one another, even before they knew they were siblings. If so, we must assume both of them would have had a “reaction” when they learnt the truth, but actually both of them seem remarkably little upset over it.
It's well known that Star Wars lead characters Luke Skywalker and Princess (now General) Leia are brother and sister. The estranged siblings didn't know about their familial relationship until "Return of the Jedi." They even shared a passionate kiss in the previous movie, "The Empire Strikes Back."
Han Solo marries Princess Leia and they have three children: twins named Jacen and Jaina, and a younger son named Anakin. Luke reestablishes the Jedi Order, marries a non-movie (but fan favorite) redheaded Force-wielder named Mara Jade, and they have a son, Ben Skywalker (named in honor of Obi-Wan “Ben” Kenobi).
The son of Han Solo and Leia Organa, Ben Solo was seduced by the dark side of the Force and renamed himself Kylo Ren: leader of the Knights of Ren, champion of the First Order, and apprentice to Supreme Leader Snoke. Driven to destroy the past, Kylo killed his father and his master, supplanting Snoke as Supreme Leader.
While on the planet, when someone asked her who she was, Rey responded by saying that she was "Rey Skywalker." Although she wasn't related to them, both Luke and Leia had been mentors to Rey throughout the sequel trilogy.
