Mirrored Background Screens on 2 of my laptops. How do I stop this?

I have a ten license pack from Norton and put it on my work desktop, my laptop and my wife's laptop (and phones).  Now if I change her display background picture it changes my laptop background pictures.  If I change mine back it changes hers.  Our 2 laptops are mirrored background display.  How can I stop this?  We both run Windows 10 on our laptops.