Team movies never, ever, ever work. The Maximum # of primary protagonists you can have while the audience still gives a shit is 3. BUT WAIT YOU SAY, WHAT ABOUT THE HOBBIT? WHAT ABOUT LORD OF THE RINGS?
Except, in the Hobbit, Bilbo is almost perpetually seperated from the dwarves during MOST of the dramatic bits. He gets seperated during the troll scene, goblin scene, in the forest, goes alone into Smaugs cave- he's the focus of the story, solo, and the dwarves are just a vehicle for him.
Meanwhile, Lord of the Rings starts with four characters (five if you count Gandalf), then add's a fifth (sixth if you count gandalf) then three more- except ONE of these is killed by the end of the first book, the hobbits split into two groups of two, and the characters people actually want to read about AKA Aragorn Legolas and Gimli (and later Gandalf) go off their own way, giving you THREE (theres the magic number again) focus's of narrative, and arguably the only characters of -real- focus are Aragorn and Frodo and the rest are supporting characters.
Avengers? It's going to suck. X Men movies? Sucked.
This one might work.
There is ONE exception. The Heist/Dirty Dozen situation. Oceans 11, Dirty Dozen (trope namer), etc, wherein you meet the characters one at a time and become introduced to them at the same time as the other characters are. No preconceived backstory, no continuity, just movie. This keeps the audience engaged.