It's just like attacking together in the old gym system...everyone does damage to the boss together (you hit, damage, friend hits, more damage), when the boss attacks, everyone takes the damage depending on your own mon...
Mostly, all you do is spam attacks nonstop...IMO, no need to dodge since the rewards are BEST for doing the most damage...You rarely will go through all of your 6 defenders unless you solo and even then, you are more likely to time out.
Dodging just lowers DPS and gets you nothing...
High damage gets you +3 balls and best team gets you +3 balls too...
If you can do the raid with less people, but same team, it's better to setup a private group since same team can give you +3 balls...(A Charizard ran from me when I only had 7 balls).
I'm not sure what determines the "Damage" category...but in larger raids, I tend to only get 1 or 2 balls in that...with my wife, I always get +3 balls.
I've done 11 raids so far...screen recorded everyone to study them and to note rewards, etc...
Also, I've noticed near every raid I start, I start 20-30 seconds late so that probably hurts my DPS a ton...