Cancer first (cause ignoring it is fatal) kids/partner second (they are tougher than you think) work third (if you can do it. If not, check your income insurance) Rellies who want it to be all about them, who make a mess, get in the way, take control of shit best left alone or reorganise your kitchen cupboards? Tell them to bugger off. Nicely at first, then more firmly then threaten them with garden tools.
If they want to help, money to hire a cleaner or someone to do the laundry would be helpful if that's the sort of thing that appeals to you. Taking the kids off your hands--under your terms-- during school holidays could be an idea. Anything that makes you uncomfortable is an absolute no go. Turn off your phone when you get home or turn it to silent and tell them not to ring you 'just to check up.' Which they are likely to do. At 9:30 pm. Gargh.
Don't let anyone needy or overly anxious anywhere near the oncology ward. Personally, the idea of anyone being in there fussing over me was enough to induce a panic attack. The staff know what they are doing and it's one of the few hospital situations where you have their undivided attention.
You will handle this the same way you have learned to deal with any other crisis, so set up support systems that suit you. Well done getting ahead of the game with the FB group. Hold your ground, ultimately this is all about you. It has to be. MXX