This is how it should be done. Set up two groups of 2 dps 1 heal, the remaining 2 dps are backups. If someone in group 1 or group 2 is voodoo dolled, one of the backup dps goes in. Any multidotting class shines in the spirit realm. People have to be vocal, especially healers and communicate who can and can't go in. You should definitely try 2 healing, it will make the fight much easier for you. Even a shadowpriest in full healing gear will be better and can still assist with healing if needed. You should try taking a combat log. We could definitely give you a bit more advice on where your group is struggling if you had a log.