If the Bible says that God raised Christ from the dead, then if Christ was just a manifestation of God in the grave, who raised Him from the dead then?
Lets handle the "if" first...
1 Timothy 3:16 KJV
And without controversy great is the mystery of godliness:
God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.
So yes, God was manifest in the flesh. Second, who raised him from the dead?
Acts 4:10 KJV
Be it known unto you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom ye crucified,
whom God raised from the dead, even by him doth this man stand here before you whole.
I am not going to ignore this verse, and there are at least 8 others that say God raised him. However:
John 2:19 KJV
Jesus answered and said unto them, Destroy this temple, and in three days
I will raise it up.
He also said:
John 10:18 KJV
No man taketh it from me, but I lay it down of myself. I have power to lay it down,
and I have power to take it again. This commandment have I received of my Father.
And you will find many other verses or sets of verses like this. Jesus said thing's like "my Father's spirit" and then claimed it was his spirit. He said the Holy Spirit would come to them and then said he himself would come to them. But for this incident, I have no problem with the Bible saying God raised him because I believe Jesus was God.
God can't exist in two manifestations at once, and Christ is your advocate, who is He advocating to - Himself?
Who says he can't? If he can't, then was there no God in heaven when he was manifest in the flesh like 1 Tim 3:16 says? Was there no God in heaven for 33 years?
My belief is that God can manifest himself in many ways and yes... Be in two different places at the same time. Isn't God "everywhere"? And with that, that is my answer to your other questions.