Question to Yone and Kha‘zix

Actually two different Questions:

1. when my opponent moves Yone in a Battlefield where i have a unit and i use (in combat) flash to save my unit. Dose the concer count as „open battlefield“ to trigger the Yone Effect and deal dmg to the unit in my base?
2. Does the Kha‘zix (Mutating Horro) when i attack or deffend Effect trigger when i play him with ambush is a Showdown that already started? (So after the normal when Attack or deffend trigger resolved) (if no: can i use ambush as reaction on a move trigger from a unit (like Hwei or traveling merchant))