You can send Diplos instead of Therizia for the 2nd Fusion Summon, but if you're running 3 Therizia and 2 Diplos, this leaves 1 of each in the deck, letting you use Domain again later.

Ash Blossom can stop Dinomorphia Domain. Use Solemn Strike or Dinomorphia Intact to protect it. You can also use Domain to bait the Ash Blossom to use Dinomorphia Frenzy without interference.