God didn't kill your family, nor does He control everything "sovereignly" or give a yay or nay as to whether or not things happen!
Nor did He make that flood come. God set some laws in motion way back when, and as a result, the flood happened. I'm not saying that God directly made the flood happen, or even indirectly. God doesn't will that any should perish. And God didn't want that flood to kill your parents. I will say this: if someone had asked/prayed for a miracle, and truly believed, something different would have happened.
And as far as not flooding the earth again, God was talking about the entire earth like He did with Noah (someone correct me if I'm wrong, please).
While we all deserve the harshest of punishments, God doesn't judge us like He did in the Old Testament. Why? Because Jesus satisfied God's wrath and paid our sin debt in full.
He also says that He will never flood the earth again in Isaiah 54:9. He isn't angry with us, and He loves us (hence He sent His Son to pay our sin debt so we wouldn't have to suffer.
Satan is equal to death, and he comes to steal, kill, and destroy. Our Heavenly Father sent Jesus to destroy Satan and his works.
Your Heavenly Father loves you. He didn't kill your family.