2 iCloud users sharing same contacts and calendar
For years now my partner and I have each had an iPhone and iPad, and we recently both got apple watches. All our devices have always used my iCloud account that I registered on my MacBook Pro years back. This used to work really well as we shared all our app purchases, iTunes music, movies and iBooks. We also shared Contacts and Calendar. In Contacts I simply created separate 'groups' for her and for me, and she told her apple devices to look at only her groups, and I told my apple devices to only look at my groups. In Calendar I created separate iCloud categories such as 'her home', 'her work', and 'my home', 'my work' and 'joint'. Again we simply told our devices to display only the category we wanted to see. We were both happy to share everything else like Photos etc.
That all worked until iOS 8 came along. Since then (and continuing with iOS 9) an issue developed where we sometimes couldn't text each other, or sms messages got delivered to the wrong devices. Calls she made or received would appear in my iPhones 'recents' list etc. And it is utterly impossible to send each other a message using our Apple Watches.
I'm pretty sure this is due to all our devices using my iCloud account, and I want to fix that by creating my partner a new iCloud account and initialising it on her iPhone, iPad and Watch, BUT I also want to continue sharing my MacBook Pro Contacts and Calendar as we do right now.
We only want to share Contacts and Calendar, Apps, iBooks iTunes music and movies. Everything else, such as Notes, Photos, Mail etc. we do not want to share. And we really want rid of the problem of text messages appearing on incorrect devices, sms messages not being sent, and us both seeing each others call history. We don't want to create separate Mac user accounts, or separate iTunes accounts etc, and want to keep the 'fix' as simple as possible.
I've searched and read loads of articles and topics, but nothing I've seen specifically helps to successfully achieve our exact requirements. I'd do 'trial and error' testing, but I understand that there's a lock on devices that only lets you change iCloud accounts once every 90 days (a possible problem as my partner only updated her iPhone and logged into my iCloud account a couple of days ago).
We'd both be really grateful for help from those in know, thanks!
MacBook Pro with Retina display, OS X Mountain Lion (10.8.5), 2.6 GHz Intel Core i7 + 16 GB DDR3