Ok so In HM and NiM KP you need to 2 tank crusher, so every other time you are tanking the enrage your shield will be up. After he finishes his enrage and goes off to charge a random raid member, the 2nd tank picks him up and he goes through till the enrage. It is very easy to do and you won't have any issues.
As to the rest of your post, My raid uses 2 PT tanks, myself and another. We have cleared KP and EV on NiM and have the timed titles for both. We are currently 3/4 in HM EC, and I can say that we haven't come into any issues with being BH tanks. You are geared for the content you are running, so that isn't the issue. Now Toth and Zorn are just beasts and hit super hard. Have you healers put on their big boys pants and get ready to heal a ton.