Hi Myra:
I don't have tremors myself, and so don't have first-hand experience. However, I wanted to write with this little bit of information:
The award-willing quilter Sharon Schamber has severe "essential tremors." I've taken classes with her, and her hands do tremble a lot. However, she's worked around her problem using a stand-up longarm machine for her quilting, and has developed techniques for machine piecing and applique that make it possible for her to produce detailed designs. Her website is sharonschamber.com.
I don't know if switching to a this type machine would help you, but I found, when I got my longarm, that it didn't require as tight a grip and steady a hand as quilting on my domestic sewing machine. Moving the longarm machine around with its handles is also much easier on my arthritic hands. If you haven't already, you could try using a longarm at a quilt show, or perhaps a local quilt store.
It's also possible using a device like her "Quilt Halo" could help you have better control when using your sit-down machine. You can see it here:
sharonschamber.com/products/quilt-halo.
Best of luck to you!