We would assume Luke would have some great resistance to the mind probe Vader gives him. The question would be if Vader detects the Force in Luke at this point, or if he ever started showing traits earlier. What if he did start showing a few years back? Would he have lessons to hide it from Alderaan, or would he have gotten training from Kanan or Ahsoka?
Or would Luke be naturally difficult to probe, like Leia deflected Riva at the age of ten with no force training.
That's another thing that I think would go more or less the same. Vader never felt Leia's sensitivity, and he was in very close proximity to her for quite some time. No reason to think it would be different with Luke. If anything, as far as the interrogation goes Luke might be less resistant since it's obvious which twin is the more stubborn and has the stronger force of personality alone.
Keep in mind that the mind probe is just a drug cocktail from the interrogation droid, not that thing where a force user can extract information.
I know that's not often very well explained, but from context clues I don't think it's actually mind-reading per see, so much as passively sensing feelings (as Ahsoka did with Grogu, and Vader with Luke in the throne room) while also imposing an invasive compulsion. Like emotional sonar; send out a "ping" and listen for an echo. Though in this case the "ping" is a push upon someone's will, and the echo is any strong feelings that float to the surface. So it's more about intuiting than "reading".
Remember that the force can have a strong influence in the weak minded, but being able to resist it just shows that a person is strong minded, not necessarily force sensitive. It's all about willpower. So of course Stormtroopers and low level Imperials are universally susceptible, while even three Jedi working together could not compel the likes of Cad Bane (though it did work indirectly as a form of torture, which incidentally is much more like how the Sith would do it.) That's probably where the mind probe is supposed to come in; wear down the subject's will so Vader can compel her to disclose the location of the rebel base.
As for the intersection with Rebels; again while the details might be different, the mission to Lothal would have worked out about the same.
Force abilities fade quickly in even those born with a strong connection, which is partly why Jedi prefer to train them young. By the time they're teenagers, both Luke & Leia had become fully formed people and had "learned" what's impossible, so while they would always have that connection; without instruction they wouldn't be able to use the force in any especially significant way. Luke got some of that instruction from Obi-Wan, so by the time he's flying in the Battle of Yavin, he's actively (but still rather minimally) using the force, which Vader then does indeed sense.
In this version of events it's Leia that would have received that instruction (and her father's lightsaber) so it should be her that uses the force and blows up the Death Star, gaining Vader's attention. However there's a slight wrinkle there since in either "timeline" (for want of a better term) Luke is still the better pilot, so why would an OK bush pilot like Leia Skywalker be jumping into an X-Wing over a known hotshot like Luke Organa?
I'm still playing with ideas, and I have a couple different notions of how Yavin might play out in this scenario. The easiest option is for simply for Luke to be Red Leader, and because they'll take anyone that can fly; Leia jumps into Red Five and they both fly the trench run, with Leia's shot finally being the one that hits the mark. Another is for Luke to be injured and unable to fly somehow, so Leia takes his spot while he watches from the control room. Not very interesting and a bit of a cop-out, but it would simplify things.
One other scenario I've been mulling over has them both flying in a Y-Wing; Luke piloting, Leia as gunner/bombardier (yeah, I know the Massassi group Y-Wings are mostly one-seaters, but it's an easy thing to alter for the sake of the story.) So it's still Leia who shuts off the targeting computer and Luke has to hold steady and trust her with Vader still baring down on them both. I kind of like this idea since it feels like the right balance of familiar and new, while letting the characters stay true to themselves in these altered circumstances. We'll see.
