Having second thoughts, I did some checking and it's perfectly OK to have a group protagonist.
Here are some examples:
After a simple jewelry heist goes terribly wrong, the surviving criminals begin to suspect that one of them is a police informant.
A group of seven former college friends gathers for a weekend reunion at a South Carolina winter house after the funeral of one of their friends.
Following the Normandy Landings, a group of U.S. soldiers goes behind enemy lines to retrieve a paratrooper whose brothers have been killed in action.
A team of explorers travels through a wormhole in space in an attempt to ensure humanity's survival.
After a space merchant vessel perceives an unknown transmission as a distress call, its landing on the source moon finds one of the crew attacked by a mysterious lifeform, and they soon realize that its life cycle has merely begun.
A group of professional bank robbers starts to feel the heat from police when they unknowingly leave a clue at their latest heist.
In a post-apocalyptic world, a family is forced to live in silence while hiding from monsters with ultra-sensitive hearing.