If it's just ramparts you tried, make sure to kill the destroyers first, they have a mortal strike debuff, and overall the mobs in Ramparts hit quite hard. (BF is a lot worse, though :P)

Your team should be able to do heroics, but you'll need to keep focus since a blue tank takes big and a lot of hits. When one of my teams hits 70 I always do a couple of kara runs with them first (with other people, of course) to leech some gear. Makes things a lot easier because you can make 'fuckups' and still be able to recover due to gear.