I'm so sorry OP - your husbands story is so similar to that of my darling brother and his wife.
He was diagnosed in March 2011 with what we thought was leukemia but after much investigation at the amazing royal marsden, we discovered it was a testicular germ cell cancer.
It had killed off the original tumor but not before secondaries had started to grow in his lymph and lower spine.
He underwent immensely aggressive chemo and radiation which did relatively little to halt its progress. He then went on 2 clinical trials before deciding to stop treatment and enjoy the rest of his time with his family and beloved wife. He passed away 8 weeks after stopping treatment and only 14 months after diagnosis - he was 28.
I won't offer any platitudes of hope because, as you know, there is no hope at this point. You already know that this year is going to be shit. Completely and utterly, harrowingly shit.
But I do know that you need to take one day at a time. Try and do one thing each day that makes you both smile, a walk in the park (my brother was wheelchair bound at the end but loved getting outside), hang out with friends, take photos of him with your dog, give him any food he enjoys. The smallest joys will help. Let your DH dictate the terms of his passing in relation to funeral arrangements - my brother was adamant that he wanted a humanist ceremony and where his ashes were to be scattered. He suggested music that he loved (he was a musician) - this was his way to retain a small amount of control over something so out of his control.
My darling sister in law is now 5 years in from his death. It has been a very long slow and difficult process, as grief always is.
Visually, i picture my brothers death as a massive raw, gaping black hole in my life. For a very long time, the hole was ragged, it left me weeping with the pain of loss. Over time, the hole was still there but the edges were less raw, they only bled occasionally. I've filled that hole with wonderful things, my children, I've filled it with things and experiences that I know would make him immensely proud of me.
The brother shaped hole in my life, it is still there, large as ever - but it's no longer raw nor does it hurt to touch. It will never close up, but it no longer fills me with dread to think about. I have no idea if this analogy will help, it did for me after he died.
I also can't stress to you the wonderful work of the Macmillan nurses. They were fantastic for my family. I live overseas so had my own grief counsellor. Talking about everything really helped me.
Try not to be too harsh with his parents ( especially his mum) - my mum behaved similarly in that she would fuss around my brother (they lived close by to him and his wife) but tried very hard not to. But it's because she felt totally and utterly helpless and lost and completely unable to protect her baby. I have a very close family and would gently remind my mum to back off a little (when word got over the grapevine to me that she was fussing). But I'm the mother of 2 children now and I understand why she behaved that way. It doesn't make it right but I understand she was trying to help the only way she could.
Please know that you can pm me any time, to rant and scream.