Morbius was part of the Midnight Sons but as a character that originated in Spider-Man and has a stronger link to Spidey than any other hero, he's probably included in the group of characters that Sony owns the movie rights to (like the rest of Spidey's villains and supporting cast).

Would be fascinating to see a full list if it existed, and how exceptions are made and which characters might be like Scarlet Witch and Quicksilver and are available to multiple parties.