I suggest having the Druids focus on healing the two tanks. You should be putting Rank 10 or 11 Power Word: Shield on everyone else for infest (start 12 seconds before infest casts). You don't need to shield the tanks. The shields will absorb the infest damage, and hopefully break all of the bubbles refunding all your mana from Rapture. They should not go below 90% health so infest will not be a problem, if someone does go below 90% then you just penance them immediately to keep them up above. The druids will be getting the tanks above 90% constantly so infest is not a problem there.
Make sure melee and main tank get away from the off tank as you go into transition. When/if the plague jumps to the OT you can just dispell it off right away and it will be gone forever.
We tank the LK on the edge in phase 1, that way we don't have to move out there for the transition.