Jesus and satan

Recently there have been many people who have been concerned with the fact that some Mormons hold that Jesus and satan are brothers. In response to this I will do my best to hold to what most Christians in general believe... or at least to what they say to believe. I refer to the Bible, and to the fact that God is the almighty creator of all things.

As far as I understand, God created all things, including every individual who has ever existed. In what we refer to as the premortal existance (http://scriptures.lds.org/en/tg/m/25) God gave every individual that he created agency, or the ability to choose for themselves. God's creations included Jesus, me, you, and even lucifer, or who we now refer to as satan (http://scriptures.lds.org/en/bd/d/35). Lucifer used his agency to choose to not follow God's plan. He rebelled against God, and was cast out of Heaven. Let me provide some scriptural references to this event.

1. Isa. 14: 12-15
   12 How art thou ^afallen from ^bheaven, O ^cLucifer, son of the morning! how art thou cut down to the ground, which didst weaken the ^dnations!
   13 For thou hast said in thine ^aheart, ^bI will ascend into heaven, I will ^cexalt my ^dthrone above the stars of God: I will sit also upon the mount of the congregation, in the sides of the ^enorth:
   14 I will ascend above the heights of the clouds; I will be like the ^amost High.
   15 Yet thou shalt be brought down to ^ahell, to the sides of the pit. (http://scriptures.lds.org/en/search?search=Isaiah+14%3A12-15&do=Search)
2. Rev. 12: 7-9
   7 And there was ^awar in heaven: ^bMichael and his ^cangels fought against the dragon; and the ^ddragon fought and his angels,
   8 And prevailed not; neither was their place found any more in ^aheaven.
   9 And the great dragon was ^acast out, that old serpent, called the ^bDevil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him. (http://scriptures.lds.org/en/search?search=Rev+12%3A7-9&do=Search)

The word brothers is taken to mean many different things to different people. When individuals proceed to dismiss the church as false because some members hold that Jesus and satan are brothers, it appears that they are using the word "brothers" to mean "one in purpose and desire." Obviously Jesus and satan are complete opposites when it comes to their purposes and desires. Jesus wants us to live with God again, he loves us so much that he gave his life for us, in order that we might have the opportunity to live with God again. On the other hand, satan wants us to suffer and to be eternally miserable like he is. Mormons do not believe that Jesus and satan have the same purpose.

Jesus and satan are brothers if you use the word "brothers" to signify "having been created by the same source." They are brothers the same way that Eskimos and Englishmen are brothers... they were both created by God, and they were both given agency to choose to do as they desired.

My question to those who dismiss both this fact and what the bible teaches in regards to this subject is: Where did satan come from? Isn't God the creator of ALL things? Could satan have spontaneously come into existence?