This is an individual journey, so my advice is to lead by example!  If you share your home with others, start by discussing your intentions of creating a safe, calm, organized future for yourself and see if they want to get on board. Begin with your own things and hopefully after your family witness the progress you are making, they may realize the benefits of surrounding themselves with only those items that Spark Joy for them. The positive impact of using The KonMari Method is inspirational.
You can train children as young as three to care for their belongings. If this is a goal for you, we can discuss it in more detail during a phone consultation.
I will work with couples/families if everyone is ready for change. You will not be tidying with each other. Instead you will each be on parallel tracks working one on one with me through your own individual tidying journey. I find that helps clients stay true to their own personal vision and joy meter without influence, judgement or guilt from well-meaning family members.