I had the same trouble before and I would hazard that all of those who did not start out typing using all fingers, are weakest on the ring and pinky fingers. The solution is practice with those fingers. If you try to think how many times have you hit keys with the middle and index fingers compared to the rings and pinkies, there is probably not even a comparison. I did two things to improve (and I have a way to go yet but I am typing confidently with all 10 right now):
1. Practice letters which you have to hit with ring finger and pinky. Do them over and over, even if it is boring and tedious. You have to develop muscle memory and dexterity with those.
2. When typing try to consciously make yourself hit the right keys with the right fingers. This will slow you down somewhat in the beginning but soon enough, even in a few days, you will start seeing a difference.

I never had a problem with this since I played the piano a couple of years before I started typing with all 10 fingers, so I don't have any pointers. Sorry. Maybe start the piano?

I do this same thing. And when I'm handwriting those fingers get uncomfortable and tired from friction.

It's because those fingers are not as strong as our other fingers, and there's little you can do about it, except slow down and deliberately hit each key with each finger until you maintain 100% accuracy and work your way up. I don't care about that though.

For a fun game and exercise try touch typing using only your ring and pinky fingers -- you'll get pretty sore, and pretty quickly, it helped me when my right ring and pinky got sore from aiming in Overwatch, since together they drive against the mouse to move it left.