How do I get my device to be the "primary?" I can on my kids' devices, which makes it really easy for my ex-husband to "join" our network and snoop my information. Is there a way to make my device (my iphone) the lead device?

How do I get my device to be the "primary?" I started the account we use, added 2 kids' ipads to the account. My ex bought an ipad and keeps trying to "piggy back" our account. I remove him from icloud, but he keeps "inviting himself back." (Just like real life-he's been nailed for STALKING and continues to do it!) Anyway, I try to go to settings on my iphone and it won't give me the option to change anything. The option is "dim" and won't react when I touch it. So, I try to do it on their ipads and I can't get it to "stick" because my ex changes the settings when they visit him. I'm about ready to throw it all away and get a totally different phone, service, etc., to protect my privacy. I want to set up home sharing instead of just having us all signing into an account, but that proves to be impossible and the operator I talked to at Apple "got disconnected" last time I tried, and after an hour of waiting and speaking to someone who spoke broken English, I gave up out of frustration, but I have to fix the problem because of the stalker.