How to get tamed wolves to not attack other players?

Wolves will not attack other players if the player and the wolf owner are on the same team.

To create a team:

/scoreboard teams add Friendly

To add players to it:

/scoreboard teams join Friendly @a

I have had this problem before, and I even went onto the wiki. As far as I'm aware as long as your friend doesn't hit you around your tamed wolves they will be friendly around them. If they are in the sitting position as most people are aware they will stay where you left them and will not engage in combat against anything that attacks you as long as you are far enough away from the tamed wolf. Hope this helps.

Tamed wolves will never attack fellow players, unless your fellow players attack them first.

In short, tell your teammate to stop punching your dogs, and you'll be fine.

This problem is common among players in multiplayer. To stop your wolf from killing your friend you have to kill your friend yourself ;) just kidding.
Your friend should sprint and run 50 blocks away from the wolf, or jump into lava/water (don't ever choose lava).
Note - never punch or hurt the wolf in reply during the activity.