Under Campaign > Solo there are 3 campaigns but 2 of them say "Coming Soon". I can play the main campaign and Old Haalayash from Spellforce 3. Am I suppose to be able to launch them from Soul Harvest as well?

If you own SpellForce 3 base game and the addon SpellForce 3 Soul harvest, the devs will rework the campaign and offer you to play the base game campaign with the new features of SF3-SH with a patch that will release until the end of this year. Just be patient. You won't miss it :wink: