Some of them will appear as cameos and some will only appear in the second film.
Spider-Man needs to be more than a cameo. He should be one of the main characters. I mean who is even the protagonist of this film? I mean it would be kind of unique if was Doom. A movie told from the perspective of the bad guy but I am not sure they would do that, even with Downey Jr in the role. If not I suppose maybe Loki. He is the guy who can sort of see into multiple worlds and connect them. In fact I I am now thinking he might be how the Fantastic 4 get to the main timeline.