How do I have any privacy on my mini iPad?
I'm sorry about what sounds like a very unfortunate situation. I would enable strong passcodes and use two step authentication. On your iPad, go to preferences and set up a strong alpha-numerical password (not a 4 digit pin) for your device in general. Since it is a new device, Touch ID should make that a minimal burden. 

Next, go to https://appleid.apple.com, and enable two step authentication on your Apple ID. 

Finally, as I'm sure would be obvious, don't share your passwords with them, and you could always enable Airplane mode every night to prevent them from having access to it over night via the wifi. 

Regarding your android, I would hope there are similar steps but don't know.