I set up a scoreboard team like so:

/scoreboard teams add Blue

Then I run the command:

/scoreboard teams option Blue friendlyfire false

Players on the Blue team can no longer attack each other.
However, players on the Blue team can still attack mobs in the Blue team.

While this might have been intentional, I am requesting a way to create an environment where all entities on the same team cannot harm each other.

Reproducing:
-Create a scoreboard team.
-Change team option "friendlyfire" to false.
-Join the team.
-Force an entity to join the team
"/scoreboard teams join @e (Team Name)"
-Attack the entity.

You will be able to harm the entity, even though both of you are on the same team with friendlyfire off.