Q: Changes on one iPhone show up on another iPhone

My family has a total of 4 iPhones, all registered to the same Apple ID.   I noticed today that my stock app lost the stocks I had originally and added Apple, Nike, and something else.  (Why my stock listings changed bothers me, but that's not the point of this question.)  

I changed it back to the stocks I wanted and had previously, and looked at my other iPhone, and watched the same change happen to the stock app on it.   I experimented a couple times by making changes on each, and they showed up on the other.

Why is this happening?   I've got thru everything I can think of in the Settings menus and can't figure this out.  I don't like the 'sharing' aspects of the common Apple ID and have deleted all that I'm aware of (Facetime, receiving calls, receiving imessages, etc).   Can someone tell me what setting I'm missing that allows these changes to be common across my phones?

Thanks

Rich