@Suzie1963 It might be a bit easier to understand if you elaborate a bit more with what's been happening.
From what you wrote it sounds like you're having a pretty rough trot.
If it was me I'd write to each of my children. Let them know how you're feeling but try doing it without blame. Something like "Your stealing from me hurts as I don't feel respected. I've also worked hard to afford to buy xyz". Letting them know that you'd like a good relationship moving forward and to start a new chapter with them could help.
If your relationships with your children are quite toxic and aren't going to change, it is healthier to say goodbye or limit interaction. Letting them know what you're doing but will have an open door if they're up for healing the relationship and building a good strong foundation.
Focusing on you and your health is very important. Stress and dis-ease aren't good for your health and cancer recovery. Being able to resolve your issues with your children, even if it's saying goodbye for a while until you can have healthy relationships with them should help. Would they be open to family counselling?
I hope that you're able to find something that helps you and them to move forward with peace