Kim - I think Grant could benefit from counselling/assertiveness training. Maybe you could go with him.

Is he afraid the kids will get mad and hate him? Let them. It's THEIR turn to feel stressed for a while and have the heat on them.

This is literally a life and death matter for him.

Most important - if you or Grant state a consequence for one of the kids, make sure you do what you said you would. Otherwise, they will keep walking all over you because they KNOW it's just words.