I agree with orion_hunters - sounds like you need some professional input here, to help understand whether working those muscles would be a good thing to improve strength, or a bad thing increasing risk of injury.
I can't go anywhere round here without taking on a hill, from my own perspective sitting is a lower stress way to climb than standing - when I'm thinking about stress on your pelvis/thighs. When I'm standing, I'm moving more of my body and putting stresses directly through my hips and knees to push the pedals down, when I'm sitting it's still hard work but it feels as though the work is coming more from my quads and calf muscles.