I’m not sure you should expect to have string 5 ring with pinky on string 6. I can do it, but it really puts my hand in an odd and very bent position. I haven’t found a reason to need that yet. Maybe someone with more experience will say something about that?
Sounds like you need to get your mind-to-finger connection working for the dexterity. this is pretty typical for ring finger and pinky. Also, the ring finger is connected by a common tendon to the middle finger, so it is difficult to move independently.
See item #3 in this to get better control of the ring finger and others: