An emphatic Yes from me. They need to know, they to have to adjust to this terrible news. You will need their help at some stage. Trying to pretend it will not happen is wrong.
In the event you might well find that you need to be the strong one, you have to keep their spirits up, yes it's true. As you weaken some of your loved ones will be unable to take the strain. If you weaken they might well fall apart.
I know this to be true.