Thanks for the thread.
I have used the same Apple ID for all five of our iPhones and two iPads and three iMacs since 2008. The reason for this was for many reasons. Initially our kids were too young to have their own Apple ID's and my wife and I found it convenient to share Contacts, Calendars, Notes etc as well as iTunes purchases. Only recently has the problem of calls from one device showing up incorrectly on other devices. The issue oddly only mixed calls and some texts on two devices, specifically two iPhones. The three other iPhones and iPads etc were never "infected" even though every setting was identical.
Family sharing came years later as an option for those that have multiple family members. This solves one issue and one issue only for Apple, iTunes purchases. However this way does not solve the issue of keeping data like contacts and notes for all members of a Family to share. As soon as you sign out an iPhone on the old "shared Apple ID" onto it's new Apple ID all notes, contacts etc are lost. So the fix that all the experts state" Don't share Apple ID" is short sighted at best.
I found threads similar to this one with the following suggestions that I have listed below.
1.Turn off Handoff button under Settings;General,Handoff & Suggested Apps (this worked for awhile until last update)
2.Turn off Wi-fi calling under Settings;Phone;Wi-Fi Calling;OFF
3.Turn off Calls on Other Devices under Settings;Phone;Calls of Other Devices;OFF
4.Ensure all numbers and emails addresses under Settings;Messages;Send & Receive only show your number and primary email and not the ones on the shared Apple ID.
5.Turn off "use iCloud" under Settings;Messages; Send & Receive; it should show "Use your Apple ID for iMessage" after turning it off.
6.Turn off "use iCloud" under Settings;Facetime; Send & Receive; it should show "Use your Apple ID for Facetime" after turning it off.
7.Turn off iCloud Drive under Settings;iCloud;iCloud Drive; OFF
I have tried 1-6 one by one and the problem of calls showing up on the one other iPhone plagued with this problem only to have the problem return. I have enacted No. 7 only yesterday. I will have to see if the problem reoccurs. I pay for Apple iCloud storage and these "fixes" are not fixes at all and I have degraded my Apple iPhone experience and capabilities severely. I will report further with additional details...
good luck...
Apple please help with a real solution. OK you want us to use Family Sharing with everyone with their own Apple ID's OK than solve the problem of those of us that didn't before and now we still need Contacts, notes etc to sync.