You see guys, there 3 big things that need to happen before Spider could join the MCU and be a part of the Civil War, but that's a topic for a different time. First ( as listed) is shattered dimensions. This is essential. First Shattered Dimentions has Madame Web
An extra dimensional being that advises Spiderman through his adventures. You need madame web because without her, there would be no way for Spiderman of our earth timeline to meet the other "Spidermen." So they go hand in hand. So this why this is relevant. In Shattered Dimensions (keep in mind this not Spiderverse) a clone of our earth Peter Parker is made. The clone (sometimes known as Krang) realized since he is an immitation of life he wants revenge on his "father" so kills Mary Jane Watson, Parker's wife. Now you may have read a different timeline where the couple is forced to erase their marriage from their mind's in order to save Aunt Mays life. Both of these story lines work but they both end up the same way (Parker loses his relationship with Mary Jane)
Next is Venom. Now we all remember Spiderman 3. A disaster, right? Yes. now moving on. We need Venom for a sinister six storyline. Well, let me re-phrase that. I think its safe to say that almost all Spiderman fans would be devastated if they left venom out of the Six. So i guess I lied, he's not essential, but he's necessary for a good Sinister Six movie.
Now the most important, The Six. Now What most people think of when they hear [Sinister Six](movie:1274281) will be the characters introduced in The Amazing Spiderman 2. But the originals were Actually Doc Ock, Electro, Mysterio, Green Goblin, Sand Man, and the Vulture. Now without these Villains there would be no actual force going up against spiderman besides the members of the Six, and minor criminals. So Spiderman needs these guys to be able to Become the Ultimate Spiderman.