Grab Thanatos if you're planning to use Shingen, otherwise you can grab anyone if you're gonna use Hercules as you can reach the def cap using Nyar, Lu Bu and Hercules's max break limit ax. If you plan to get Thanatos, there's no need for Hercules as you can reach def cap without her, meaning you'd be better off with Shingen. Regardless, I'm sure you can clear the current content with either souls and whomever you get as long as you level up your grids.

Though I don't recommend tickets on Hades or Amon. I personally only use Hades for her atk down and Amon's only use is her -25% def down, which in that case you'd be better off just getting Satan for her -15% def down and -10% dark res which is basically the same.