stay away vs keep away; "pass away" vs "fade away"

A. Is there any difference between “stay away” and “keep away” ? Take a look at the following sentences:

1. Several children had to [color=green]stay away from school because of the bus strike. - Could I substitute “stay away” with “keep away” in this one? why/why not?

2. They say that the Old Manor House is haunted by ghosts, but I think it’s only a story to [color=green]keep children away. - Could I substitute “keep away” with “stay away” here? why/why not?

B. Would it make any difference if I substituted “pass away” and “fade away” in the following sentences?

1. “Old soldiers never die, they simply[color=green] fade away” (an old song) I guess that “pass away” would be as good as “fade away” here…

2. Grandpa passed away recently - “faded away” ? By the way - why isn’t there “HAS passed away” ? I mean… we use present perfect for recent happenings… don’t we?

Best wishes!

If you notice any mistakes, I would be grateful for correcting me.[/i]

‘stay away’ and ‘keep away’ have nearly the same meaning but different usages.
We use ‘stay away something’ but ‘keep somebody away’ or ‘keep somebody away from something’

I think ‘fade away’ is more formal than ‘pass away’