The words of Jesus you cite, “The kingdom of God is within you,” is from Luke 17:21 and was delivered to the Pharisees. A better translation is provided in the RSV Catholic Second Edition:
Being asked by the Pharisees when the kingdom of God was coming, he answered them, “The kingdom of God is not coming with signs to be observed; nor will they say, ‘Lo, here it is!’ or ‘There!’ for behold, the kingdom of God is in the midst of you.”
Given that the question came from the Pharisees who largely opposed him, it’s difficult to think that Jesus meant the Pharisees had embraced the kingdom of heaven. Even his closest disciples, including the apostles, had not yet been baptized, by which they and all Christians become “temples of the Holy Spirit” (1 Cor. 6:9), i.e., in which God and the power of his kingdom dwells with us.
Given the time frame in which Jesus spoke his words, “the kingdom of God is in the midst of you” refers to his being the King and that he was in their midst advancing his kingdom through his teaching, including the Sermon on the Mount, and the signs and wonders that also illustrated what his kingdom would be like. So Jesus was teaching the Pharisees and others that the kingdom was available to them, within their reach, if only they became his disciples. It’s an implicit reference to their made in the image and likeness of God (Gen. 1:26-27), and that they thereby had the God-given ability to cooperate with God’s grace to make the kingdom of God a reality.