Recount will be accurate enough for the purpose you're trying for. As long as none of your characters is out of range of the combat log, recount will catch all of their damage. You can set recount to display a graph of combined dmg or dps, and it will list each characters separate damage and DPS, making it easy to add them up for a total. Not only that, but you can click on each character listed under recount and it will break down their dmg by spells/dots etc.