Although I am a huge fan of the clone wars star wars really picks and chooses the superpowers of the force. A lot of the time I can justify it. And as we've seen before, just because you can wield the force, it doesn't mean that you can see all and do all. Vader never even considered leia to be kin until he sensed that Luke was hiding something.
But the lightsaber always seemed like it was symbolically important to the Jedi. Like using your Dad's baseball mitt. They were heirlooms. Antiques.
Which is why Kylo would want Anakin skywalkers lightsaber. Because he was buying into the iconography of Darth Vader.
But as far as Luke sifting through the debris of the deathstar to find the kyber crustal belonging to Vader? (For one thing, it exploded in all directions, there is a very slim chance that it made it to endor) it sounds like uncreative fan fic. Or at the very least a comic book side quest.
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Regardless how you may feel about it, it is established in canon that Jedi can sense Kyber crystals. So it's not an unreasonable in universe conceit assuming it happens.