Try going in alone rather than as a pair - you should be able to do it as either class. Done it as ret/disc when looking for some transmog stuff, haven't taken my shammy yet but it should be doable.
The tomb does 104% health as dmg so you need to cast a heal which does 5% of health or greater, while the person is tombed. And it happens over a 4sec window - which should be plenty of time for you to cast a couple of heals. If you don't make the heal, have you tried just carrying on instead of wiping - it will take longer but should work
Classes with passive damage reduction will not die as long as they are at full health on the first frost tomb, without needing heals. This applies to at least warlocks with soul link and a pet out. If you have the opportunity spec into things such as cheat death for this fight.