How to prevent changes on the iPad
Apple's Parental Controls can restrict many things.

If that's not enough you can create profiles with Apple Configurator that allow additional restrictions.

You could also teach your family members how to fix the settings they changed accidentally. Give one of them the messed up iPad and tell them the steps to do. If they don't remember next time, make them write down the things to check. Print out the checklist and stick it to the back of the iPad.