Hi, I know I will probably annoy allot of higher level members by telling you why your devices aren't behaving as you want, and how to solve it, because I think they know the work around but want to force you to separate your iCloud accounts, or they actually don't know how to solve this. Either way I will probably annoy them.
First of all its not a bug, its the way iCloud has been designed. The culprit is a master call log file that resides in iCloud Drive. Each device that is logged in to the same iCloud account and has "iCloud Drive" enabled will sync to that master call log. Nothing else affects this, FaceTime, continuity, cellular phone call forwarding have no affect no matter if they were on or off.
The only work around possible at the moment, until Apple redesigns how its iCloud service behaves at their end, is to accept that iCloud Drive functionality will not be available and should be turned of for devices that you do not want to sync to the master call log in iCloud Drive, to do this you have to follow these instructions carefully:
1- Keep iCloud Drive turned on for the devices you want the call list synced across, and turn it off for the devices that you do not want to sync with the master call list.
2- Most importantly, even if you turn off iCloud Drive for your iPhone(X), but you still find the recent call list from it appearing on your other iPhone(Y) that has iCloud Drive enabled, the culprit is that iPhone(X) is syncing its call list with iCloud Drive indirectly through another device that is linked to it via either the same FaceTime number or via enabling calls on other devices and at the same time has iCloud Drive enabled. For example your wife's phone list is appearing on your phone even though you have iCloud Drive disabled on your wife's phone, the culprit is that your wife's iPad or iMac, has iCloud Drive turned on, and at the same time is linked with the same FaceTime and phone forwarding settings with your wife's iPhone, so your wife's phone is syncing its call list with her iPad, and then her iPad is syncing that list with the master call list in iCloud Drive, because iCloud Drive is enabled on her iPad. The solution is to disable iCloud drive on all devices(iPads, iMacs etc...) related to iPhone(X)'s FaceTime and phone forwarding settings.
3- Eventually you should end up with two phone ecosystems on the same iCloud account for your devices, those devices, iPhones, iPads, IMacs etc... that have iCloud drive enabled and have the same FaceTime and phone forwarding settings. And another set of Devices that have iCloud drive disabled and at the same time are linked together with a different FaceTime number/Email and phone forwarding settings.
4- Delete the recent call lists after you go through these steps on your iPhones.