I think Ariel will be Featured this month and Poseidon on September.
It’s impossible to be sure with the Ursena big 
in the Atlantis featured scheme.
HOTMs seem to be clear by now, but Atlantis heroes are hard to Predict. I’d say Ariel + Mok or Ariel + Missandra though. With Khiona and Musashi
Poseidon + Missandra (or Mok) on September along side Aegir and Alby
All we can do is speculate though 