We have done these already and my answers were:
my legacy to mother earth: my legacy to mother earth wouldn't be any material thing. I hope I can help her in saving trees,plamting, participating in every program that involves taking care of her. and I hope my participation and cooperation would be a legacy too.
to people: I would be a good influence to them. and a role model too.
to my family: I would give them an honor for them to remember my legacy.