I have to say, and I don't mean it badly, but I think you chose the wrong instrument. It sounds like you both don't have a nack for the technique, nor the physical build to ever achieve what you want. It really something to consider, because if you are indeed very musically gifted, and you feel like you were meant to do it, that will come through on whatever instrument you're playing, maybe you would be the best violinist ever? I have met many many frustrated students (not mine!) who find themselves running inti a wall of where nature will allow them to go, and it never works out, but it does usually end in debilitating Carpal Tunnel Syndrome.
But aside from that, don't focus so much of your wrist and elbows. Elbows should just hang, only to mive out sideways as you go up the keyboard, like wings. They should just hang loosely from your shoulder. If you just focus on always keeping your shoulders relaxed and your arms hanging, stiffness will be impossible. the problem with having very small hands though, is that once you try to play quick octaves or chords, it will actually be impossible without a degree of stiffness because the stretching itself causes stiffness! I would never try to play a fast run of tenths, for instance, because I know how I would have to strain to do so.