You can not create objects during runtime.
You always create an instance (of an object) during runtime.
Assuming dat we speak about animated sprites, then every sprite will have one unique object assigned to it.
Every object needs to be in the layout before runtime.
Therefor, create a placeholder object for every sprite in the layout. Assign a sprite to it from the array during an 'on layout start' event.
(if you want a .cap from that stap, then post de .cap with the array)
Then it is easy to use Construct's family-pick-system to create random things. As in this .cap