Moq –
“Again, it seems clear that one must kill oneself before killing someone else”
Don’t you mean allow oneself to be killed rather than killing someone else?
“I have wondered why the Poskim have a universal ban on Euthanasia; if suicide is permissible in the face of torture and certain death (an opinion held by many Poskim)”
Perhaps the poskim in question do not hold permissible suicide when facing certain death.