How can I lock the settings on a Galaxy 8?

I have elderly parents. My father in law has tremors and tends to change settings when he doesn't mean to and then in an effort to fix it completely disables the phone. This results in having to wipe his phone and reset it 2-3 times a month. I do not have an Android and have searched but I am not finding anything that will lock the settings so they cannot be changed. I would also like to lock the phone so no additional apps are installed as he has signed up for pays services unknowingly a few times. Is there an app that will allow either of these features? Locking the settings would be the most important as we can remove the credit card info from the phone and stop the charges.

Thank you in advance for any suggestions.

Welcome to Android Central! Try a kid-safe launcher like Kids Place. Obviously, it's intended for kids, but it could also be useful for your parents. It can limit their interaction to certain apps, and will prevent them from accessing the settings or the Play Store. It requires a PIN to exit, so there shouldn't be any easy way for them to accidentally go back to the stock launcher.