My uncle has lung cancer. We're not exactly sue how bad it is, but its serious. I'm trying to avoid telling my cousins who are younger than me, but I feel slack them not knowing. My mum is having a hard time coping and so is my aunty. My grandparents dont know whats going on exactly, but hey have an idea that my uncle is sick. He has a test soon to see how bad it is, and if its really serious, well...
I hope for the best-case scenario. I think you should let your uncle decide who he should or shouldn't tell. You're doing the right thing not telling your cousins yet imo. But he will have to tell in the near future; he can't hide it from his kids forever.
I wish your uncle the best. <3 Let them find out how bad everything is before they tell the children; there's no reason to worry them if it's still in a treatable state. Support your mother the best you can. My uncle died recently and my mother had a very difficult time dealing with it, but you just need to comfort her.