How does Reva know about Leia and her ties to Obi-Wan? Like, it’s a secret even to Vader that Luke has a sister.
The connection is Bail. He was a strong supporter of the Jedi and Obi-Wan is last seen on Bail's ship. There's no one else around with ties to Kenobi from the prequels (unless they can dig up Jar Jar), so it makes sense that you kidnap Bail's daughter or wife to try to draw Kenobi out of hiding. I don't think that's a stretch, but I think it's odd that you would send a spy/bounty hunter/inquisitor to follow Bail after the kidnapping to find out where Kenobi is hiding. If you think Bail is the connection, then why not track him to find Kenobi's hideout and catch him off guard? I would have liked to see Bail contact Kenobi remotely or at least throw on a disguise. Heck, if Reva can read minds why even both with Leia - just go trap Bail and find the Kenobi connection.
If the inquisitors were younglings, they’re all 17 year olds.
Maybe not an official youngling, but Reva could have been pre-teen and is now in her lower 20's. I would buy that. I did read somewhere that the Inquisitors were all fallen Jedi and I think Kenobi confirmed that in his dialogue. Vader supposedly trained them too, so either by some form of recognition or him simply saying who he is, I'm not surprised the inquisitors know his former name.