Neither the account in Matthew 12 or Luke 11 have the Pharisees casting out demons. The crowds saw Jesus cast out demons and wrongly concluded that if the demons obey His command He must be their ruler. Jesus refuted them.
What we can learn from these versus is that demon possession is real and that casting them out is an act of mercy, one of the fruits of the Spirit. That you would ascribe them to Satan only speaks to your motivations.
You are more lost than I realized if you believe that only God’s workers can cast out demons. Satan can and does all the time. In churches all around the world. Grab a crucifix, a candle, a bottle of “holy” water, a rosary, and a book of exorcism rituals and believe it’s God’s work. When the finished work of Christ is not even believed or accepted for salvation in those churches, yet they still believe that God is with them. The only one being truly helped by that is Satan.