I get asked this question quite often “Should Family Members or Business Partners Sign an NDA?” An NDA is best to use no matter who you are discussing your idea/product with. When you say don’t worry about family you can trust them. Consider does your family know as much as you do about how to treat your idea/product and keep it confidential? Do they know about public disclosure and how that can hurt you? Having them sign an NDA pushes the point that you are taking this seriously and they need to respect that and not tell your neighbors about your idea/product unless you agree it is okay to do so.
The same goes for anyone you are in business with and plan on showing them your idea/product. It sets the tone for everyone that you take this seriously and you want to keep it private. I work with a lot of Inventors and can tell you from experience showing your idea/product to family and friends is not a great indication of whether your idea/product is a winner. Most family members will not want to hurt your feelings so you will mostly get positive feedback from them. Which can cause you to spend money needlessly.
You need people that you trust to give you brutally honest opinions of your idea/product. It is not hard to find people that love everything you show them. You want people that give honest opinions and you need to not let those opinions hurt your feelings or take it out on anyone that tells you your idea is not that great.
I have done idea/products reviews for a living for a number of years and the Inventor is quick to want to shoot the messenger instead of taking a hard look at why they got a rejection. I have shown Inventors several products already on the market that are better than the one they are swearing is a million dollar idea and all they can respond with is that doesn’t matter theirs will still be worth millions. You need to make informed decisions based on facts, not what you want to happen.