If you tell the truth, you're giving these people the opportunity to break away from their usual pattern of bad actions (if there was any), and get into the pattern of right actions. If they don't know how, then help them the best you can.
This would be sharing the Dhamma. If these people aren't buddhists, then don't be obvious about it (like, "Dad... this is what I think the Lord of the Shakya Clan, the Perfectly Enlightened One, would recommend us to do in this situation..." etc.) Just pointing them in the right direction would be good enough.