I guess you would have to have access to the initial agreements to know this kind of stuff but I would assume that Marvel retains the rights to the Miles Morales character. I'm not exactly that up on comic book stuff but isn't Morales a fairly recent creation and a character that hadn't even been conceived when Marvel sold the rights to Sony back in the 90's?

I guess they could've conveyed the rights as Spiderman, Peter Parker, and all future alter-ego's of Spiderman but that seems kind of unlikely to me. And if Marvel still has the rights to Morales I can't imagine they would convey them to Sony just for the rights to get Spiderman to do guest spots in their already massively successful string of movies.

Sony is already on their third attempt and building a sustainable Spiderman franchise, why give them access to a new character with his own set of storylines for Spiderman?