Can Christians have demons? We overestimate Satan and give him too much time and power.
If we trust in Jesus' words than we know that if Jesus dwells within us through the Holy Spirit then God is the strong man within not Satan.
Matthew 12:28,29 28 But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.29 Or else how can one enter into a strong man's house, and spoil his goods, except he first bind the strong man? and then he will spoil his house.
We are tempted by Satan through the flesh. God does not tempt us. John 8:47-4947 He that is of God heareth God's words: ye therefore hear them not, because ye are not of God.48 Then answered the Jews, and said unto him, Say we not well that thou art a Samaritan, and hast a devil?49 Jesus answered, I have not a devil; but I honour my Father, and ye do dishonour me.
When we honor God we are His. How can we be God's and Satan's?
1 John 4:1-3 4 Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.2 Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:3 And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
The antichrist is anyone who is against God. If the Spirit of God which Jesus baptizes us with does not dwell within us then we are not of God. It is Satan that dwells within the un-believer. He is their strong man.
1 John 4:13-15 13 Hereby know we that we dwell in him, and he in us, because he hath given us of his Spirit.14 And we have seen and do testify that the Father sent the Son to be the Saviour of the world.15 Whosoever shall confess that Jesus is the Son of God, God dwelleth in him, and he in God.
1 John 4:4 4 Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.