To make the 4th and 5th finger stronger, start not compromising the 2 fingers. Always make sure they stand firm on their fingertips, means when you press down on the finger joints, they won't collapse.
When practising running notes and thrills, play them from knuckles, practise to play from knuckles first. Make sure the palm is in C shape, then by lifting up the fingers high and play loud in the beginning with firm fingertips, until the knuckles can be felt and the pianist feel in total control of the fingers. Don't compromise on this part especially the pianist has weak "bridge". Don't lock up your wrists, if not knuckles won't have strength.
BUT To play running notes smoothly (only later on): don't lift up finger higher than the surface of keyboard, so that the fingers can run.
When playing octaves and chords, the top note must be louder than the bottom note. Keep whole arm relax and free from tension always.
Slowly with a lot of time, conscious and patience, you will be able to overcome. In order to develop a new habit, you have to keep conscious and alert at all times, and practise it slower for fully control.
That's all, wish you all the best luck!