Q Our neighbors gave us a set of their keys, just in case. Do I have to give them ours?
A Nah -- not if you don't want to. In giving someone a key, you're in effect saying "I trust you not to go to our house and look through our most personal things while we're away." If you don't feel that way, don't give 'em your key. There's no need to explain your choice, no need to give excuses. If they come right out and say "You can give us your key if you want," just offer an effusive thanks and tell them that your friend/cousin/mother already has your spare and leave it at that. Then put away their key for safekeeping, and go back to being the good neighbor that you are.