Big hugs. I had someone very close to me die last year. Here are some thoughts:

Children are actually a lot better a dealing with death than we expect them to be

Might be an idea to organise a family photo session while he is still relatively well.

In terms of help, I really appreciated the people who just got in and did something. It's really frustrating to get the "if there is anything we can do to help..." line. Most people are very unlikely to say "oh I would love a meal or some help with the cleaning". Much better to unobtrusively help.

Food is always helpful - not having to cook is always a blessing!

Flowers always cheer things up.

As others have said, they need normal too.

Make sure funeral details (don't forget cremation/burial), will, power of attorney etc etc are all sorted well in advance.

Find out what palliative care options there are, especially if he doesn't want treatment. People don't have to be in agony at the end - there are some amazing drugs out there. You also don't want to be in a position where no-one has medical guardianship (or whatever it's called) and so a hospital is obliged to prolong life when it's not what he would have wanted.

I hope he has a dignified journey.