I've been diagnosed with cancer twice, 20 years apart. I learnt a lot about human nature that has stood me in good stead. People's reactions do vary greatly, and you can't be totally responsible for them, and some will heal with time. For instance, my in-laws never visited me in hospital. Not because they didn't care, but because they hated hospitals. although that was not something they could voice. I had to learn to manage my expectations of other people so I was not plagued by disappointment. Obviously your in-laws reaction is far more drastic and harder to manage.
The second time I was the person who could be accused of treating my own parents poorly. They are now elderly and require a high level of care when visiting (from 1000k away). They wanted to visit, but with a bilateral mastectomy, rapidly being followed by chemo, I couldn't cope with their requirements as well as support my children and partner. There were some painful conversations that took some months for everyone to really get over, in denying them their 'right' to visit.
The most critical relationship and support is between yourself and your husband. When I was diagnosed early last year my partner and I had only just committed to living together two weeks prior, and he had moved from interstate to do so. I took two actions to provide him with the support I knew he'd need. I called a few appropriate close friends and explained that the support I needed was them supporting him and providing some specific direction on how they could do that. For my partner it was calling him to have a chat, but for others it might be the pub for a chat. There are many variations. The second was giving him a role of communicating news to friends when I felt incapable. This meant he was talking to people early on and sharing feelings. Appropriate support for your husband may be something entirely different of course.
Good counselling is great. It can be hard to find and to fit in, and hard to get a partner to accept though. Keep talking to each other. Share your fears and confusion, but be clear that they need not be his burden; just things you need to get off your chest. Acknowledge that neither of you will be playing Superman or Superwoman roles this year. It will be super just to get the kids to care and provide a meal at the end of the day. I learnt to keep my opinion of how the kids were dressed (although I still don't understand how they ended up with dresses on back to front) or their hair done, or even if the food was healthy.
Good luck and take care.