God is all powerful, omni potent, all knowing and ultimate being. No one can question him. His capabilities are beyond our reasoning.
Eg. If God wants to forget something he can forget it completely. And if he wants to unforget what he forgot he still can do it. So practically God is ultimate beyond our understanding. Even the angels cannot have even 0.00000000001% understanding of God.
Ok. Now coming to the point
Does God know that Lucifer ,adam are going to sin.
YES
SIN can consume us in our self, in our house, in the garden of Eden, even in heaven . But no matter where it is. Sin cannot co-exist where God lives. Be it in your heart or in heaven. Either God leaves or Sin is expelled.
Killing of people in floods and wars
It may sound in-human because we are restricted with our human extent of thoughts.
Death is final , end for us.
For God, death is like a sneeze. There is life after sneeze right?
God can forgive your sins when you live in earth or even after death or even a minute before the judgment.
God do punish us with difficulties to make us understand the situation and it's result. But he'll or eternal death is our choice 100% our choice not even Lucifer will take the responsibility. Satan influence us and induce us to sin, but we wantedly sin on purpose knowing the wages of sin.
Jehovah, Jesus, holy spirit are 3 in 1.
Holy spirit guides us to live perfectly in our mortal life, jesus bridges the gap between us and Jehovah. Jehovah is the ultimate prize forever
Death by itself is not sin
Eternal separation is called death
We have to die for sin and live by christ
Which leads to eternal life with Jehovah
If we die in sin and live for the world
Which leads to eternal death/separation from Jehovah