I just brute-force Bron and ignore the shards since most of the time he seems to call the shards off my melee guys, so it's always a long fight. I just save my cooldowns for the last 30% and keep it slow and steady for the first part. With 3 locks, I imagine you have time to get some pain off with 3x CoD.

Ick I kite the whole time, letting him do his piddly melee damage to my tank while my DPS chews on his butt. I could probably stand still and do the strafe thing, but why screw with what works? Earthshield and Riptide easily negates any damage I take. you could alter my riptide macro for Rejuv or shields. I've got mine up to rolling 3 riptides and I drop Flameshock in instead of purge for mobile fights like this. Again, 3xCoD could work nicely here for you, Dots and pets can do the rest until you get a feel for places where you can stop and get a few casts off.

Garfrost is all about the strafe. Zoom your camera all the way out {allll the way, I had to go into options and set my max camera distance to high for a lot of the new bosses} so you can see what's going on. I can't fight him on the stairs as some people suggest because my DPS tends to lose LoS or get stuck, so I fight him in the middle until the stun, then gather everyone up and take a trip behind a rock or down the stairs to clear the debuff. If you've got DBM, you should get a warning and I think you get a raid icon on the person he's throwing the boulder at. You should be able to see a shadow, just strafe away from it.