IPhone – FaceTime launches on the Macbook when I have incoming phone calls, even though I’m not logged into iCloud

It's a bit of a drastic move, but why not delete the preference files for FaceTime? This should put FaceTime in an uninitialized state (at least for preferences, perhaps not for configured accounts).

Close FaceTime, click on the Finder, then hit the Go menu and choose Go to Folder….

Enter ~/Library/Preferences into the box and press enter. Look for any files that start with "com.apple.facetime" and move them to another folder (for backup purposes).

Open FaceTime back up, check your preferences, and see if the Auto-Accept continues to occur.

Yes - this technology seems to be driven by your contact card info stored by calling party. If calling party has info for you and someone else in same contact card, then both phones will ring for FaceTime even if not same Apple ID.

In our case, we had friend who had stored my number and husband's number (not email) under my contact card. Both our phones would ring when friend tried to FaceTime me, even though husband and I have separate Apple IDs and caller never selected the other number.

Solved it by having calling friend remove the additional phone number from my contact card on his machine.