I would be ok with Ezra being Reys father and his mother was Sabine and Ezra has been prisoner all this time and Luke has done nothing out of fear until rey gives him back his courage he had when was younger.
The chances they use any character from the cartoons in a prominent roll in the episodic movies is extremely small. Especially two such important characters in the cartoon. They included Saw Gerrera (Forest Whitaker) in Rogue One, but this is a spin off movie, and a minor character from a single story line with little to no background story to have to adhere to.
As far as any of the main characters I would bet on ever seeing them in the new movies, because they will never make the cartoons, books, comics, or any other secondary medium a necessity for understanding characters in the episodic movies.
Casting calls for the Han Solo movie implies that Sana Staros (And not Solo) from the second volume of Jason Aaron's Star Wars will appear, probably retelling the story in which Han had to fake mariage with her to pull off a robery in a casino. However, since it happens BEFORE her appearance in the comic, reading "Showdown on Smuggler's Moon" is not necessary to understand who Sana is.
As for the theory that Ezra could be Rey's father, I don't think he'll be. He's a main character from Rebels, not a bit part from TCW. Saw Gerera doesn't need much background to appear in RO, Ezra would if he'd appear in the Sequel Trilogy.
The Han Solo movie is not one of the Episodic movies, so the interest in this will be by people who are more inclined to have read or viewed the supplemental material from the cartoons, comics, and books. While I think it's a great idea to have some of these spinoff movies, I don't really consider them to be a true part of the main story. They are side bar material, and for the somewhat more hard core fans.
This group of fans is far more likely to know of Han's relationship with Sana, and all sorts of other EU-esq material.
Probably, yes. And ideally, Sana appearing in the movie will finally kill those cries of despair from those who only saw her reveal and never bothered to search more (And thus learn that they never actually married) But you're right about the Anthologies/Stories being side stories. And I hope they'll be good (I'm far more afraid of Han Solo than I am of Rogue One)
For that to have any chance of possibly happening, Sabine would not give birth to Rey for another 20 years in the Rebel's timeline. Have you taken that into account?