They take time, especially in the early going. They are still very much the wild birds of Africa and behave accordingly.
One time with my first flock I had an Ag guy on the property to help with soil issues we had there. Up comes the flock, they surrounded us, screaming and complaining loudly. They were incensed that someone they didn't know was on their property.
I asked him to wait a moment and walked away from him calling "birds." They followed me to their pen where I gave them a millet treat, closed the door and walked back to the guy. He was floored, he said I had no idea you could get Guineas to do that.
But it took time to get them to that point, they were less than a year old and still quite the crazy teenagers.