Sorry to hear that @ComaChameleon
I know we are taught to respect our grandparents (and parents) but they need to realise you and your brother are of age to look after yourselves.
You do have to remember though that they both are still grieving. They have lost a son and now a daughter in law.
Probably best to have a gentle word without falling out. You all need each other after all? 
Old age doesn't always come with knowledge or respect. Respect is a two-way deal. You must give respect in order to receive it whatever your age. With age doesn't come automatic respect.
Like @Cleoriff says @ComaChameleon you have to make your grandparents understand that you and your brother are adults and no longer need supervision. Politely but firmly. If that doesn't work tell them to f*** off. Harsh but sometimes you have to be harsh to get your point across
@ComaChameleon you need to start as you mean to go on. You're an adult and have been for some time. Your mum didn't check up on you, so why should your grandparents? You have to make them understand that.
Sorry to hear that @ComaChameleon . It must be so painful. Hope you feel better soon 
