hello
@Perry13
a warm welcome from me too
your grandparents are fortunate to have such a thoughtful grandchild
I think your Nan will appreciate knowing you are there for her - though be aware that she may be shielding you from how it is for them 24 hours a day, it's hard for anyone who doesn't take on the main carer role to fully understand, so maybe just say to her that you'd like to try, and want to help in any way you can
might you do small tasks for her eg offer to do some shopping or help her do it online ... just happen to make a batch of stew (or any meal, or cakes, favourite puddings etc) and tell her it's too much and would she help you out by taking some ... spend time with your grandfather so she can have a few hours to see a friend or go for a walk ... do her ironing, say it's a secret santa thing or you need the practice (sometimes people find it hard to accept help, so try to turn anything round to say she's helping you) ... say you can't afford a Christmas present so could you come and do the vaccuming/any house work once a week/fortnight next year ... offer to take on admin tasks for her .... drive her/them to appointments and take them for coffee
whatever you offer, make sure you keep to it and on your Nan's terms ... it's so frustrating to be offered lots of help that doesn't materialise, but a few things that happen on time as agreed can make a very real difference