Well, they'd have intimate information about him and the Nazis that they could give the Allies, information which might still be useful even though the war was over. Then there is the matter so-called honour and feeling it would be better for his family to endure death than life with the enemy. Those are the reasons as a Nazi he might have chosen to kill them, the "noble" reasons.
But him being human and prone to human acts of selfishness, then he could also have not wanted his family to have something he could not have for himself, which was a sort of freedom.
Goebbels had the incredible power to maneuver military units. He began campaign strategies and pushed for even more civilian sacrifice. But Germany was already on the verge of collapse and his greatest efforts were in vain.
On dismissing his colleagues when he sensed the end was near, he said,"When we depart, let the earth tremble!" He spent his last days with his family in the Fuhrerbunker under the Chancellery. Following Hitler's execution, he disregarded Hitler's direct orders that he succeed as Chancellor.
Instead, on May 1, 1945, he had an SS doctor execute his six children by lethal injection and had an SS orderly shoot him and his wife. With the egocentricism and pathos that constantly surrounded him he said shortly before his death,"We shall go down in history as the greatest statesmen of all time, or as the greatest criminals.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.