Does Power Cosmic work with only one member of the team?

I'm not sure what you're asking. The Power Cosmic Team Ability reads:

"Members of this team do not take pushing damage and their powers cannot be countered. This team ability cannot be copied by wild card team abilities."

The figure must have this team ability on it's dial in order to use these powers, just like any other team ability, and these powers cannot be copied using a wildcard, like Minions of Doom or Spiderman Ally.

You may be confused by the wording of "Members of this team". Read this as "Figures with this team ability".

Hope that helps!