Well, Ms. A, you can try all sorts of trickes to get the family on board, but the easiest (and most peaceful) thing is to declutter the areas you care about, give them some space of their own (I shut my son's bedroom door for years, for example), and just do what you need to do to declutter your space (which might include the main living areas, too.)
You can try a yard sale and everyone gets to keep the money they make from selling their own clutter. (If they help with the sale! LOL)
You can get together and agree on clutter-free zones. But, again, you'll still probably have to take their clutter back to their area often until perhaps they get the message.
I have found it more peaceful to just compromise on what matters most. For instance, I have books and magazines that were always called clutter when I wanted everyone to clean up their clutter. I still have many of them. It's not clutter to me! LOL But, I would limit what I had in the living areas to what I called reasonable just to have everyone else pick up their socks and glasses and jackets.