Nail biting is hard to stop from the outside (I too am a long time nail biter). If anyone told me I had to stop - including me - it wouldn't work.
What does work is a good multi-vitamin to calm the nervous system. The fact that everyone in your family bites their nails is an indication that you are all nutrient deficient. Find a high quality multi-vitamin to give to your kids daily (in the morning). Take one yourself and notice a huge difference in your propensity to bite your nails.
And give up on changing the behavior for your children... it won't work. Just don't let them do it in public.
P.S. Hot sauce or THUM on the fingers is abusive and dangerous. Not only does it burn the mouth, they can get it in their eyes, which is dangerous as it can damage the eye tissue. It will also cause more nervousness as their fears become elevated by the trauma.