Want someone to change a behavior? Frightening them with a harsh and loud voice, threatening them, or punishing them is what most have learned to do. It comes from a place of love and concern. But the fear created will always lead to hatred in hearts. Fear can never create love. Instead, it destroys the love that ever existed in the heart of the one receiving it.
Fear can only create short-term results. They might obey you out of fear in your presence. Even then they might be cursing you under their breath. Once they are out of your vicinity, they will definitely do what you don't want them to do. The heart never trusts the one who frightens it. It feels as if this person doesn't like me being happy, thus, they are restricting my happiness. This in turn will create a thought that everything restricted is actually something that gives them happiness. Throughout life, they try to do things that are labeled 'forbidden'. They find happiness in defying, defying those who had disrespected them and hurt them. They just can't understand how these forbidden things actually harm them.
Here the problem is, only we see the consequences, not them. We make the decision for them and force it upon them. Each time you force something on someone, even if it is something that benefits them, they will hate doing it their entire lives because they have a negative feeling attached to it. This is the reason why I don't force my children, i.e., I don't scold or spank them, to study. If I frighten them, they would hate studying. 'Studying' would become the reason they were hurt. Hence, they would never be able to enjoy it nor feel they 'need' it. Instead, they will try to get away from it. The same goes for anything you want to inculcate in their lives, with force and fear.
Let them decide for themselves. Inform them of the consequences, both sides. "What will happen if you do this", "What will happen if you don't do this", and then "What do you want to do now?". Talk of the benefits, show them how you too do it passionately and they will fall in love with it too.