spoilers for Rebels season 4
I think time period is an important factor in this.
Kanan, Ezra, and Ahsoka all worked with the Rebellion, but none of them did so at the same time as Luke.
Rebels takes place fifteen years after Revenge of the Sith, four years before A New Hope, where Luke joins the Rebellion. Despite the pervasiveness of the Rebellion across the galaxy, we can see Luke doesn't have an intimate knowledge of it from Tatooine. And, this is a bit more of speculation on my part, but I don't think the Empire would be making a concentrated effort to let every planet know that there are two Jedi in the Rebellion - that would make it seem as if they had a chance.
So I think it's fairly safe to assume that, before A New Hope, Luke wouldn't have known about the Rebellion Jedi.
First, let's talk about Ahsoka.
You are correct in mentioning that Bail was in direct contact with Ahsoka and worked with her. However, in season 2 of Rebels, Ahsoka is seemingly killed by Vader. Even when Ezra saves her in season 4, it seems clear that Ahsoka is joining Sabine to find Ezra, not rejoining the Rebellion.
And then there's the person she worked the most closely with - Bail Organa. Who, in A New Hope, died on Alderaan. Luke never met him, so he couldn't hear about Ahsoka from Bail.
(I'll mention Leia in a bit.)
Now, onto Kanan and Ezra.
At the end of Rebels, set two years before A New Hope, Kanan dies and Ezra disappears. They were prominently working in the Rebellion, and it is confirmed in the Marvel Star Wars comic series that Hera is a general in the Rebellion at this point. But, in this series, set between ANH and ESB, she never interacts with Luke or the crew.
Again, this is a bit of speculation, but I don't think that any of the Rebellion fighters who knew about Kanan and Ezra would have mentioned it (Again, I'll mention Leia in a bit). First off, here's the thing about Kanan and Ezra - as much as they helped the Rebellion, they're both just gone now. It wouldn't really help Luke to tell him "Yeah, there were these two Jedi with us a while back! Oh yeah, and then one died. And the other just sort of disappeared, we don't know about him. But no, good luck with your training!"
This is sort of working with negative space, but the Marvel Star Wars comic series never mentions Kanan or Ezra. And I think that, if they were ever going to be mentioned to Luke in the canon asofar, that would've been it.
But then there's the sticky wicket - Leia.
For Ahsoka, I think I want to say that she didn't know about her. Maybe Leia would've met Ahsoka at some point through Bail, but then Ahsoka "died." But with Kanan and Ezra - Leia did directly meet them, and knew that they were Jedi. But then they were both gone, too.
Leia never mentions Kanan or Ezra in the Marvel SW comics, but - and again, this is speculation - I think it's a safe bet that she would've at some point mentioned them to Luke. But - and here's another guess - I don't think she would've done so within the original trilogy.
Luke is training to be a Jedi while Leia, in the comics, is annoyed with him for seeking that over helping the Rebellion. Even when she does encourage it, why would she tell him about the previous Jedi? She probably thinks they're all dead by this point - not only would that not help Luke, but it would probably make him think that he'd just end up dead or that he doesn't have anyone to turn to to help him train.
I looked on Wookiepedia, and I can't a place where Ezra was mentioned in any of the Skywalker-era Star Wars stuff. Honestly, I think it's a pretty safe bet that Leia would've told Luke about Ahsoka and Kanan and Ezra at some point, but I can't find any evidence of her actually doing so, and I don't think she would've done so while they were still fighting.