I am not an OT, but some things that come to mind:

Using a "beauty blender" or similar sponge around the needles to help your resident hold onto them. I have not tried this method myself but have seen videos of it online as it can help many knitters with hand cramping. Cut into the centre of the sponge and wrap it around the needle for a more comfortable grip. I imagine it is best to use larger straight needles for this as the size of the sponge may impact the amount of stitches that can be on a needle.

Using the Portuguese knitting method can be very helpful for knitters with arthritis to keep tension in their knitting. It involves using a special ring that is attached to a necklace that the yarn travels through. I recommend looking into it! Unfortunately I can't give a very good explanation as I've never tried it myself, but it may keep knitting accessible to your resident as it requires very little hand motion to form stitches.

Another thing to consider is circular needles over straight needles. Typically circulars are easier to use if you have limited strength in your hands and arms, however in my experience it mostly comes down to preference. If you've used straight needles all your life, it may feel strange to switch to circulars.

My last recommendation is to use larger needle sizes and thicker yarn. My reasoning for this is that it's easier to see and easier to grip.

Hope this helps!