Unlink my devices

Updated to latest IOS as well as changing three iPhone 6 to iPhone 8 and now all my devices are linked. Backed up all to iTunes as well as iCloud under the one Apple ID and now when we change something on one phone it changes on all three devices. How do I unlink these but still keep the devices on "Find My Phone". Do I need to setup all these devices with separate Apple ID's? Need help please - thanks