That's only true if the developers belong to a publisher, and even then, there are exceptions. In this case, it's not true at all. Nintendo might have bought exclusivity rights for the game release, but that's about it.
Not necessarily. The publisher doesn't have to own the studio to produce the game their making. Sony produces the Ratchet & Clank games, but they don't own the developer, Insomniac, who are independent, Sony does own the IP though, so Insomniac can't do anything with Ratchet & Clank without Sony's approval.
|They also can't call the shots on a brand like Marvel. Here, Marvel, and by extension Disney, calls all the shots. And remember how they reacted after the Battlefront II debacle with EA?|
Marvel Games has some level of input, but it's the publisher who's mostly in charge. Spider-Man PS4 for example, is owned outright by Sony, with Marvel simply licensing the character to them. Same with Ultimate Alliance 3. It's Marvel, but it's Marvel licensed to Nintendo. Or the Fox X-Men franchise in the case of film.