Doctor Octopus and the Goblin are obviously in from the trailer, and it seems pretty clear that Sandman and Electro will be as well. The Lizard seems to briefly appear in the trailer as well. Venom would make number six, and obviously Vulture is still alive, although presumably still in prison.
I don't think this is going to be a straight up Sinister Six situation, though. Doc Ock and Sandman, as I've mentioned previously in this thread, seem far more likely to fight with Spider-Man than against him given how their respective stories ended in the Raimi movies. Electro, Goblin, and Lizard seem likely to fight against him. Venom is probably somewhere in between and may shift loyalties over the course of the film. James Franco may have been cancelled, so I doubt we see him in the film.
I don't see Morbius appearing in Far From Home, as he hasn't been established yet. Hell, we don't even know if Venom will be in the movie, or if the tease at the end of Venom 2 will lead to Tom Holland moving from Marvel to Sony. Or it could be both. Who knows?