The problem of only spawning 1 box is because inputs are only executed once and only at one place.
It’s getting the first actor spawn actor, executing your input and ignoring all other actors which want “read” the input too.
To solve this, first turn off all “Auto Receive Input” on all actors including the controlled pawn, go to Edit Menu → Project Settings → Input → and add a Action Mapping, on the example, is “INPUT_SpawnActors” with the key 1.
On your main character blue print, you need to do this:
