To me from scripture it doesn't seem likely that someone can have the Holy Spirit and a demon simultaneously but I'm willing to have an open mind here.
Be under the influence of both simultaneously, no. They will either be following the leading of one or the other.
Let me say this: The question I think you are trying to answer is, if a person is baptized in the Holy Spirit will it of necessity cleanse every part of them, i.e. every area of their heart, from demonic influence. I honestly don't think it happens that way. I take outpourings and infillings as just that, outpourings and infillings. During a time of outpouring the Spirit will dominate the person's actions, heart and thoughts. But as you know, the Spirit of God can be grieved and can also be quenched, and once it is quenched whatever has not been cleansed that was evil may start rising to the surface again.
I think many think in terms of absolutes - sort of like applying Calvinist thinking to the Holy Spirit - but I don't see it that way. James wrote to the early church less than 15 years after Pentecost, and in his letter he warned:
1 My brethren, let not many of you become teachers, knowing that we shall receive a stricter judgment. 2 For we all stumble in many things. If anyone does not stumble in word, he is a perfect man, able also to bridle the whole body. 3 Indeed, we put bits in horses’ mouths that they may obey us, and we turn their whole body. 4 Look also at ships: although they are so large and are driven by fierce winds, they are turned by a very small rudder wherever the pilot desires. 5 Even so the tongue is a little member and boasts great things.
See how great a forest a little fire kindles! 6 And the tongue is a fire, a world of iniquity. The tongue is so set among our members that it defiles the whole body, and sets on fire the course of nature; and it is set on fire by hell. 7 For every kind of beast and bird, of reptile and creature of the sea, is tamed and has been tamed by mankind. 8 But no man can tame the tongue. It is an unruly evil, full of deadly poison. 9 With it we bless our God and Father, and with it we curse men, who have been made in the similitude of God. 10 Out of the same mouth proceed blessing and cursing. My brethren, these things ought not to be so. 11 Does a spring send forth fresh water and bitter from the same opening? 12 Can a fig tree, my brethren, bear olives, or a grapevine bear figs? Thus no spring yields both salt water and fresh.
13 Who is wise and understanding among you? Let him show by good conduct that his works are done in the meekness of wisdom. 14 But if you have bitter envy and self-seeking in your hearts, do not boast and lie against the truth. 15 This wisdom does not descend from above, but is earthly, sensual, demonic.
This was written to Spirit-filled people. When he asked, "
Does a spring send forth fresh water and bitter from the same opening? 12 Can a fig tree, my brethren, bear olives, or a grapevine bear figs?" the teaching was not that it was impossible (as the context bears out, given he was implying that a believer can let demonically-inspired words come out of his mouth), but rather that it was unnatural; that we are born of a holy nature, so it would be unnatural to allow something unholy to come from a holy source. But again, the context suggests he is saying that this can indeed happen, and we must not allow it to.
I don't know your friend, but it sounds like he's the real deal, only the spirits that empowered his witchcraft have not been fully dealt with yet, and need to be. Reminds me of Simon the magician, who clearly still had his demons as well, given that Peter warned him, "I perceive that you are [still] subject to the poison of bitterness, and the bond of iniquity." The man still had his demons and had not dealt with them.
Pray for him. It's not always easy cleansing the soul and spirit completely, and for some it takes many years, especially if the demons he allowed in before coming to Christ were exceptionally powerful, and ones he very much was at home with and not wanting to part with completely.
