If your wife loves to kayak, I have a tip for you. My husband got a tow rope -- it is stretchy and has clips on both ends. He leaves it attached to his boat, and when my arm gets sore and needs a rest (a problem I've had ever since my mastectomy), he tows me for a bit. Then we unhook and I paddle on. He is in great health, and this allows us both to get out and enjoy nature. I had to get over the fact that I needed to accept help, and that other people may feel I look lazy. We have learned to make modifications in our lives so that we can continue to do the things we love.
I am praying for you and your wife. Cancer is a terrible disease that is just as hard on the caregiver as the patient.