Unsync two devices

iOS devices do not "sync" to each other, so I'll assume you have used the same Apple ID on each. This makes them both sync to your iCloud content.

Use unique Apple IDs on each.

It didn’t work. When I changed my Apple ID on my iPad I saw it immediately doing the same thing to my iPhone. It’s as if both devices think they’re one

Nothing Apple allows will create this.

There is no remote control app or settings like you are describing.

What software might your work phone have installed on it?

I'm having the same issue with my iPhone 6 and iPhone X. I want to give the iPhone 6 to my mom, who's in an extended care facility. I created a new Apple ID, changed all information and changed all information on the iPhone 6. Now, however, my iPhone X shows her information, including new Apple ID, birthday, etc. So I suggest you stop saying what Apple does or doesn't do and provide a valid solution because your customers are experiencing the same problem.

My intuition is telling me that maybe I need to start the whole process over. And contact Apple so that I can make these devices separate. Perhaps when I initially set up my iPad I transferred all the data which included all alerts that would be similar to syncing it.

Sync vs nonsync that is. I want the devices to be separate entities. Right now whatever I do with one seems to happen with the other.

It didn’t work. When I changed my Apple ID on my iPad I saw it immediately doing the same thing to my iPhone. It’s as if both devices think they’re one

I just changed my Apple ID on my iPad as you suggested. And then it was changed immediately on my iPhone. I am perplexed. This sink non-sink thing is very confusing. Please advise