1 John 4v2 say that everyone who accepted Jesus Christ is of God the devils accepted Jesus Christ in Luke 4v41 are the devils is of God too?

Answer 1

1John 4:2 is speaking specifically about the people seeing prophetic visions, and since demons would deceive them "Masquerading as angels of light" and tell them things contrary to God's will, the writer is saying to exercise caution and test the "spirits", because if they were indeed "of God" then they would acknowledge Jesus as Lord.

But in the case of Luke 4:41, the demons were cast out of a crowd of afflicted people and were exposed before him, but why they exclaim that He is the Son of God I am not sure. If you remember the case in which He cast "Legion" into the herd of pigs, it is very possible for demons to plead for mercy, so it is very possible that they were yielding before him as though they were humble, but as for "Being of God", they did not and could not repent, nor accept Him as their lord, for they were bound to Satan and his fate.

The devils knew who Jesus was, since He is the eternal Son of God and almighty creator, who was only on the earth in order to die for the sin of the world. Their acknowledging this did not mean or imply belief or allegiance, just a factual knowledge. They were subject to Him in the sense that He had (and still has) power over them as almighty God.