If you're not running instances at 70 with this group, there's no need to specifically spec healing on any of them. I'd go with a prot pally as a main, since the AoE spec works so well with large groups of standard mobs. Have the fury warrior /follow and go for primarily whirlwind/cleave/AoE attacks. Have the elemental shaman provide support with windfury totem, magma totem, heal/mana stream totem, chain lightning, & chain heal when needed. You could even try having the prot pally on /follow, since it's a fairly low-maintenance build, and keep the fury warrior as your main.. I wouldn't bother making the paladin a holy-spec or shaman a resto spec.