Is this normal that when I kill Scyla and she spawns the Mindfraggers I cannot see them as they are blocked by the Scyla’s dead body?
I think this could be the case. Not experienced it myself, but Id not be surprised.
What I have experienced is mindfragger being spawned into small terrain pieced that couldnt be destroyed so I had to restart the mission.
I have two cases involving Chirons:
First, wherein I killed one and it dropped onto the POI and I could not access it anymore. There was no way to finish the mission and I had to redo it.
Secondly, when it sent some fire worms and it landed onto some destructibles. I could not access the worm and needs to destroy the object first with grenades.
To answer your question, yes, it is possible that those big aliens CAN drop on others to cover them.
Big enemies like the Chiron and Scylla, become map props after they die, you can even use their body as cover, AND, you can also destroy with gunfire or explosives.