I'm so sorry. It is ok to allow yourself to feel whatever you're feeling. And it's ok if that changes a lot and goes back and forth. 
For him, I think the most important thing is to be led by him. Do not take away any more control over his life than this diagnosis has already taken away from him. Offer support where he wants it, and help with the things he's doing to feel a bit in control again (e.g. The wills stuff).
Don't try to impose your own vision of how you think he ought to feel or act or spend his time. "Positivity" is helpful to some, but to others feels isolating ( "nobody understands how awful and frightening this feels") or like being given false hope.
For you, my advice would be to have the conversations you've put off or never gotten around to, and the same if there is a musician or place you've always wanted to see together but never quite got around to (not necessarily massive bucket list type stuff, but maybe there's one or two things you'd wanted to do that haven't yet happened)... Tell him you love him. Tell him how much he means to you. Having heartfelt conversations in the early days can be too difficult, especially if you're not used to it, but it becomes easier. Tell him how you feel, don't assume he knows. It is ok to cry together, for him to see you hurting and comfort each other - to be there for each other. Being with each other as you cry can be a way to connect.
There is a balance to be found between trying to find a way to be present in the moment (e.g. Just sitting drinking coffee with him and soaking the moment up rather than worrying about other stuff or mentally planning dinner) and being mindful of not leaving yourself with avoidable regrets in the future (e.g. Wishing you'd told him he inspired you to do xyz). Having both in the months to come will help you cope now and when he's not here anymore.
I don't want to frighten you but please be mindful that "time left" is very far from an exact science. He might be here longer than estimated and I would love that to be the case for you all, but he might be here much less. He also might not be well enough to do some things in a year. So don't put off things that are important to say or do because you're banking on him having two years.
I know it's mentally protective to tell yourself you don't need to face them yet and keep putting them off, but bringing them forward and prioritising them is a way you can feel slightly more in control in the face of this horrible, shitty thing that's happening.