Why can I not stop sharing iCloud, as opposed to deleting it, which I believe will affect other device? For example, my apps r showing up on his phone, but his stuff is not coming to mine. If I delete my iCloud, am I also deleting his? All under same account.
If you are talking about the App Store, the important thing is the AppleID you used to sign in. Assuming two devices both signed in with the same id, the default behavior is: when you make a purchase on device A, it is installed on device B at the same time. Downloading an already-purchased app does not propagate. Deleting an app does not propagate. iCloud data associated with the app is not deleted if you delete the app from only one device.
You can disable the "purchases installed everywhere" choice from the Settings > iTunes & App Store page.