MTG can you destroy a chosen sacrificed creature twice
In both scenarios, you would be unable to cast the second Murder because the Aerie Ouphes has already been sacrificed. Since they no longer exist, they can't be targeted.

Because Aerie Ouphes have Persist, they could very well return the battlefield before they even deal their damage, and you could target the new Ouphes with Murder, but that won't prevent the original Ouphes from dealing their damage.



You seem to think that responding to an activated ability is to do something before it has been activated, but that's wrong.

There are two parts to getting the effect of an activated ability:


First, the ability must be activated (or copied).
Then, the ability resolves.


In between activating the ability and it resolving, players will get priority (possibly more than once). To respond to the ability is to do something after the ability has been activated, but before it resolves.

Costs to activate an ability are payed when activating the ability, so paying the activation cost happens before one has a chance to respond to the ability.

The cost to activate an activated ability is found before the ":" in the ability. That means that sacrificing Aerie Ouphes is part of the cost of activating the ability, and therefore happens before one has a chance to respond to the ability being activated.



Note that everything I've said here also applies to spells (cast, then resolves) and triggered abilities (added to the stack after being triggered, then resolves).