I have to use separate accounts if I want "Find my iPhone" to work. But can't use separate accounts to share data. So I switched to DropBox for data.
Since we bought extra memory for my wife's iCloud, my iPad signs on to her account. That allows me to back it up to the cloud (I wish there was a feature to back up to computers & iCloud without manually switching).
But I can't do that with my phone, so my iPhone only backs up to my Mac - and keeps warning me "Storage Almost Full You can manage your storage in settings". Settings on-line and on my phone both say I have 717 MB, with iCloud Drive, Backup, & and mail turned off. Notes is also turned off, which is a real, real pain - my wife want to share our notes and calendar, and I have to have my iPad with me to see them.
I guess I need to return my Mac to using her iCloud account, and only have my phone on my iCloud account - only so it can be used for "Find My Friends", and have its calendar and notes be useless.